0:00:00 > 0:00:06I'm climbing over 300 ft above the River Avon in the Avon gorge near Bristol.
0:00:06 > 0:00:09I'm just a small part of what's being suspended
0:00:09 > 0:00:12from one of the engineering marvels of the Victorian age.
0:00:12 > 0:00:15This is the Clifton Suspension Bridge.
0:00:15 > 0:00:19This is Climbing Great Buildings, and throughout this series I'll be scaling
0:00:19 > 0:00:25our most iconic and best-loved structures, from the Normans to the present day.
0:00:25 > 0:00:28I'll be revealing the buildings' secrets and telling the story of how
0:00:28 > 0:00:34British architecture and construction developed over 1,000 years.
0:00:46 > 0:00:51This time, my journey through Britain's great buildings brings me to Bristol.
0:00:51 > 0:00:55Complete in 1864, Clifton Suspension Bridge was designed by the most
0:00:55 > 0:00:59famous engineer of the Victorian age, Isambard Kingdom Brunel.
0:01:01 > 0:01:06Today it's the earliest complete surviving example of a suspension bridge anywhere in the world.
0:01:09 > 0:01:14When the idea was dreamt up, the Clifton Suspension Bridge was to be the world's tallest and longest
0:01:14 > 0:01:18suspension bridge - typical bravado in the age we've come to call
0:01:18 > 0:01:20the Industrial Revolution.
0:01:20 > 0:01:23Its completion marked a milestone in engineering history.
0:01:23 > 0:01:28It's more pure engineering than any building we've seen so far.
0:01:28 > 0:01:31But the materials it used and the structure it perfected
0:01:31 > 0:01:36would come to influence architecture well into the 20th century.
0:01:38 > 0:01:41In order to get a closer look at this iconic example
0:01:41 > 0:01:48of Victorian engineering, I've been given unprecedented access to see the bridge from a totally new angle.
0:01:48 > 0:01:53I'll be climbing out of Brunel's towers to get close up with the Victorian ironwork...
0:01:53 > 0:01:58It's amazing, isn't it, how this long after it was dreamt up, it still seems
0:01:58 > 0:02:00an amazing achievement.
0:02:00 > 0:02:03Getting caught in the rain over the Avon Gorge...
0:02:03 > 0:02:05It's a tad moist.
0:02:05 > 0:02:10And getting a totally unique view of the bridge by dangling 250 ft in the air.
0:02:10 > 0:02:16That actually brings home, doesn't it, the audacity of taking on a project like this.
0:02:16 > 0:02:17Three, two, one.
0:02:19 > 0:02:24Joining me as ever is the queen of British climbing, Lucy Creamer,
0:02:24 > 0:02:26a team of riggers
0:02:26 > 0:02:30and intrepid all-action cameraman Ian Burton...
0:02:32 > 0:02:36to see how the tenacity of a visionary engineer went on
0:02:36 > 0:02:39to create a structure that inspired modern bridges the world over.
0:02:47 > 0:02:55Isambard Kingdom Brunel was only 24 when he entered an open competition to design the bridge in 1831.
0:02:55 > 0:02:58He called it his first true love,
0:02:58 > 0:03:00but it wasn't a simple process of construction.
0:03:00 > 0:03:04It had everything that a Victorian melodrama should have -
0:03:04 > 0:03:09it had conviction, love, loss, disappointment, and ultimate triumph.
0:03:09 > 0:03:16It remains today the only substantially complete early iron suspension bridge in the world.
0:03:21 > 0:03:26The bridge spans 702 feet across the Avon Gorge, with Clifton and Bristol
0:03:26 > 0:03:30on one side and Leigh Woods in North Somerset on the other.
0:03:33 > 0:03:38For the first climb we'll be scaling the bridge's West Tower, on the Somerset side,
0:03:38 > 0:03:42to see how the structure of this feat of engineering is supported.
0:03:42 > 0:03:47I'm excited by this. It's a truly iconic structure.
0:03:48 > 0:03:51It is about the most perilous position we've climbed in so far.
0:03:51 > 0:03:56In any normal building, this would be ground level, wouldn't it?
0:03:56 > 0:03:59But this ground level is about 300 ft over a gorge.
0:03:59 > 0:04:07With this wind and the cars going by, you can actually feel a slight wobble going on.
0:04:07 > 0:04:10The bridge does wobble. It's got that expansion joint down there.
0:04:10 > 0:04:12Of course, the bridge has to flex.
0:04:12 > 0:04:15It has to give a little bit because it has variable weights on it.
0:04:18 > 0:04:22You see that wonderful great sweep of iron chains?
0:04:22 > 0:04:24- Yeah.- It was built top-down,
0:04:24 > 0:04:28so the chains get built first, and everything gets hung from it.
0:04:28 > 0:04:34As it's called a suspension bridge, you've got to build the thing from which everything is suspended.
0:04:34 > 0:04:37So up we go, then, and see the bones of this thing.
0:04:45 > 0:04:48It's a fair breeze that blows up the gorge.
0:04:48 > 0:04:50There is, yes.
0:04:50 > 0:04:52- Look at that boat chugging up there. - I know!
0:04:52 > 0:04:55- It's picturesque, isn't it?- It is.
0:04:55 > 0:04:58It's a pretty little natural wonder on the edge of a city.
0:04:58 > 0:05:03- This is actually where I started climbing.- Is it? - And it's where I went to school.
0:05:03 > 0:05:05- You're a Bristolian?- I am, yes.
0:05:05 > 0:05:11- This bridge just holds lot of memories for me, having seen it from a very young age.- Fancy that.
0:05:11 > 0:05:15Yeah, it's really cool for me to be up here now.
0:05:15 > 0:05:18- So this is your stamping ground. - Yep, it is.
0:05:22 > 0:05:26So, Jonathan, when they were thinking of building a bridge across here,
0:05:26 > 0:05:32why didn't they just go for the traditional big stone aqueduct-type design?
0:05:32 > 0:05:35In the 18th and 19th centuries,
0:05:35 > 0:05:43Bristol, its goods were carried in the great sail ships, clippers, those kinds of boats.
0:05:43 > 0:05:48So if you've got broad sails, and in particular tall masts,
0:05:48 > 0:05:51you'll need something like 100 ft clearance from the water.
0:05:51 > 0:05:54So you need very broad, very tall arches.
0:05:54 > 0:05:59- So I think stone was out - too bulky, too expensive, too big... - Yeah.
0:05:59 > 0:06:04and iron was in, but iron was still an audacious leap forward.
0:06:16 > 0:06:20I have to say, I'm really enjoying being up here.
0:06:26 > 0:06:28A suspension bridge is a fairly simple shape.
0:06:28 > 0:06:31But it's juggling with some fairly elemental forces.
0:06:31 > 0:06:33It works more or less like this.
0:06:33 > 0:06:35I'm going to put in two towers first.
0:06:35 > 0:06:38That's the sequence they were built in, after all.
0:06:38 > 0:06:40So there are two towers.
0:06:43 > 0:06:46And the chains
0:06:46 > 0:06:55go more or less like that, and then there are rods coming down from those chains.
0:06:55 > 0:07:00Those rods carry what they hope to be a fairly flat deck.
0:07:00 > 0:07:08The problem is, there's enormous force down there, trying to make this lot sag. And so,
0:07:10 > 0:07:13to either side,
0:07:13 > 0:07:18there are more chains, which are anchored into the ground like that.
0:07:18 > 0:07:26So the force which tries to come down here and sag down into the middle is held back
0:07:26 > 0:07:29by these forces creating an equilibrium which is balanced
0:07:29 > 0:07:35on each of these towers, so this position here is really important,
0:07:35 > 0:07:41in each case, in holding the whole thing together and stopping it from plunging down into the gorge.
0:07:45 > 0:07:46Let's away, lady.
0:07:46 > 0:07:49- Yeah.- There's more climbing to be done.
0:07:49 > 0:07:50We're not going away yet.
0:08:09 > 0:08:14By the 19th century, Bristol had undergone a boom in building and population.
0:08:14 > 0:08:18It was one of Georgian and Victorian England's busiest ports, seeing much of the goods and
0:08:18 > 0:08:22sea traffic coming in from the colonies of the British Empire.
0:08:23 > 0:08:27At this time, Bristol's only bridge across the Avon was in the city centre.
0:08:27 > 0:08:31The only option in crossing the gorge was to take small ferries,
0:08:31 > 0:08:35but a successful entrepreneur had a plan to change all that.
0:08:35 > 0:08:38The original conception was of a local merchant, a man called William Vick.
0:08:38 > 0:08:40And why build a bridge?
0:08:40 > 0:08:45The theory is that William Vick thought it would be useful for the rich and famous to be able to get
0:08:45 > 0:08:49to the clean, fresh air of Somerset without having to go down through the
0:08:49 > 0:08:52docks and the rather smelly hoi polloi of the docks area.
0:08:52 > 0:08:54And so a competition was held.
0:08:54 > 0:08:56What were the circumstances of that?
0:08:56 > 0:08:59A competition was advertised and 22 designs were submitted,
0:08:59 > 0:09:03including four by this young man, Isambard Kingdom Brunel.
0:09:03 > 0:09:08But because of the technology involved, they asked Thomas Telford to act as judge for the competition.
0:09:08 > 0:09:11Telford dismissed all 22 designs, said that they wouldn't work,
0:09:11 > 0:09:14and Telford said, "Here's one I prepared earlier."
0:09:14 > 0:09:17He effectively submitted his own design and awarded himself
0:09:17 > 0:09:19first prize in the competition he was supposed to be judging.
0:09:19 > 0:09:22That smells like a bit of a stitch-up. What did Brunel do?
0:09:22 > 0:09:25Brunel got the judges together about two miles from here,
0:09:25 > 0:09:31harangued them for two days, and they withdrew the original announcement and gave the prize to Brunel instead.
0:09:37 > 0:09:43The first part of the bridge to be built were these huge foundations, called abutments.
0:09:43 > 0:09:45Built into the rock of the Avon Gorge,
0:09:45 > 0:09:49they give the towers a firm footing on which they still stand today.
0:09:53 > 0:09:56Because there are no detailed construction drawings,
0:09:56 > 0:10:00it was thought that this abutment was solid, until some routine
0:10:00 > 0:10:08maintenance work on the pavement discovered a shaft which led down to 12 hidden, underground chambers.
0:10:12 > 0:10:19Discovered in 2002 after being closed up for over 150 years, these enormous vaults beneath
0:10:19 > 0:10:23the two towers were built to reduce the cost of construction.
0:10:23 > 0:10:29It meant that less stone needed to be used without reducing the abutment's strength.
0:10:30 > 0:10:36The reason all this is thought to be sold it is because a borehole was driven in 1969 to investigate it.
0:10:36 > 0:10:42It just happened to hit solid wall and so they thought it was pure masonry.
0:10:42 > 0:10:45But today, you can come in here and see these grand spaces. Look at it.
0:10:45 > 0:10:48Fabulous. Thousands of stalactites.
0:10:48 > 0:10:49It's a spectacular thing.
0:10:49 > 0:10:54And you can see where these man-made vaults meet with the natural rock.
0:10:54 > 0:10:57In fact, there are two vaults here running parallel,
0:10:57 > 0:11:02and then through that wall there are another five at 90 degrees to us.
0:11:02 > 0:11:05Incredible engineering achievement.
0:11:05 > 0:11:08And of course when Brunel died, the fact that
0:11:08 > 0:11:16there were no notes and no drawings meant that the secret of these spaces went to the grave with him.
0:11:18 > 0:11:22Brunel's hidden vaults are around 36 feet in height but are linked by
0:11:22 > 0:11:26tiny holes only just big enough for a man to crawl through.
0:11:26 > 0:11:29But in 2002, the first man to come down here
0:11:29 > 0:11:33in over a century and a half took a slightly different route in.
0:11:33 > 0:11:37John, what happened when you discovered these vaults?
0:11:37 > 0:11:40It was round about sort of March time.
0:11:40 > 0:11:42I got a call asking me to come and survey the shaft.
0:11:42 > 0:11:49As I came in the shaft and looked through the hole - I had a powerful head torch on -
0:11:49 > 0:11:53and saw this blackness and then my light going through, I thought "wow".
0:11:53 > 0:11:59I then crawled through and there it was, the first of the chambers.
0:11:59 > 0:12:03And what did you think when your light fell on these great vaults?
0:12:03 > 0:12:07It was just amazing. Every time we found a new chamber, we thought "blimey!"
0:12:07 > 0:12:10So was there anything left by the builders?
0:12:10 > 0:12:12Nothing at all, which is really disappointing.
0:12:12 > 0:12:17We really hoped to find some stuff, but a couple of nails and that was it.
0:12:17 > 0:12:20Nothing whatsoever. It was completely clean.
0:12:24 > 0:12:31Brunel completed these huge abutments in 1836, but it wasn't plain sailing from here on in.
0:12:31 > 0:12:33Buying the iron chains needed to span the gorge blew the budget
0:12:33 > 0:12:39and a disappointed Brunel had to call a halt to construction in 1843.
0:12:42 > 0:12:43This bridge will always be remembered as one of
0:12:43 > 0:12:50the seminal monuments to Isambard Kingdom Brunel, but few realise that it was completed after his lifetime,
0:12:50 > 0:12:54this structure that he'd called "my first love, my darling".
0:12:54 > 0:12:59When he died in 1859, building work had stopped for some 16 years,
0:12:59 > 0:13:04and it was the Institute of Civil Engineers who appointed two of their number to complete the task.
0:13:04 > 0:13:07Enter Messrs Hawkshaw and Barlow.
0:13:07 > 0:13:11It was they who managed the completion, who oversaw it
0:13:11 > 0:13:16and who ensured that Brunel had a lasting legacy in this bridge.
0:13:16 > 0:13:22It took just two years for Hawkshaw and Barlow to complete the bridge and, 33 years after construction
0:13:22 > 0:13:27had begun, Brunel's dream of a suspension bridge spanning the Avon Gorge
0:13:27 > 0:13:31was finally ready and open to the public.
0:13:31 > 0:13:36The bridge was originally intended to carry only light horse-drawn traffic.
0:13:38 > 0:13:45Today, largely unchanged since the 19th century, it carries over four million cars a year.
0:13:47 > 0:13:53For the next climb, we'll be scaling that Clifton Tower, gateway to the Bristol side of the gorge,
0:13:53 > 0:13:59to see how a Victorian technological innovation made carrying all that weight possible.
0:13:59 > 0:14:04- What I want to see up there is a saddle. Sounds unlikely.- Right.
0:14:04 > 0:14:06- Bridges have saddles.- Do they?
0:14:06 > 0:14:08Another place for you to sit.
0:14:08 > 0:14:14Bridges like this do because there are 11,000 cars a day come over this bridge.
0:14:14 > 0:14:18Much more than Brunel ever imagined.
0:14:18 > 0:14:22- But the reason they can take the load is to do with this saddle.- OK.
0:14:22 > 0:14:24So I think it's worth having a peek at.
0:14:24 > 0:14:26Definitely. I'm intrigued.
0:14:26 > 0:14:29How high is it over the gorge?
0:14:29 > 0:14:32From the actual bridge level, about 250 feet.
0:14:32 > 0:14:36- This is going to be the highest climb we've done, in that case. - Yeah.- Yeah?
0:14:41 > 0:14:43Wey!
0:14:43 > 0:14:46- It's getting a little bit windy now, isn't it?- It's picking up.
0:14:46 > 0:14:49At this sort of ten foot off the ground altitude.
0:14:49 > 0:14:52Suddenly we're in the wind zone.
0:15:01 > 0:15:03It's a tad moist.
0:15:03 > 0:15:06Well, yeah. It's Bristol. What do we expect?
0:15:06 > 0:15:08- You've got to embrace that west coast atmosphere, haven't you?- Yeah.
0:15:08 > 0:15:15Hey, while we're here, do you want to pass the time with a little game of spot the difference? OK.
0:15:15 > 0:15:18Cos this tower is different than that one in a few subtle ways.
0:15:18 > 0:15:20They look identical to me.
0:15:20 > 0:15:24Three big differences. I'll give you one cos you can't see it from here.
0:15:24 > 0:15:27On the sides, the sides of this one
0:15:27 > 0:15:32are scooped out by these arches, but they're solid in that one.
0:15:32 > 0:15:34That's just one difference. Two more.
0:15:34 > 0:15:37OK, something to do with the top?
0:15:37 > 0:15:40- See the arch?- Yeah.
0:15:40 > 0:15:42It's much more pointed on that one.
0:15:42 > 0:15:45It's much more like a Gothicky arch.
0:15:45 > 0:15:48This one is rounder.
0:15:48 > 0:15:49But there's one really clear difference.
0:15:49 > 0:15:54If I slap the corner there and give you a clue.
0:15:54 > 0:15:55That's a good hand hold.
0:15:55 > 0:15:58A nice sharp arete.
0:15:58 > 0:16:00You climber! What about that one?
0:16:00 > 0:16:06- Ah, yeah, it's looking a bit more of a flat surface.- It's shaved off.
0:16:06 > 0:16:11It's a chamfered corner. 45 degrees diagonal slice off the edge.
0:16:11 > 0:16:14- Less of a good hand hold for you. - No, that wouldn't be good.
0:16:14 > 0:16:16But it gives the tower a different profile in each case.
0:16:16 > 0:16:20From a distance they look the same, but they obviously learned from them as they made their way upwards.
0:16:20 > 0:16:25You can see big joints in the masonry right the way down to the floor
0:16:25 > 0:16:29where bits have been added and they changed their mind.
0:16:29 > 0:16:33- The rain's setting in, Lu. - Right, shall we find the saddle?
0:16:33 > 0:16:36Yeah, let's get in there.
0:16:39 > 0:16:44I tell you what. Even though it's raining, we've actually got quite a nice view.
0:16:44 > 0:16:45It's a heck of a view, over Bristol.
0:16:49 > 0:16:51- So is this the saddle?- There it is.
0:16:51 > 0:16:54- Look at that beauty.- That's amazing.
0:16:54 > 0:16:56It's massive.
0:16:56 > 0:17:00From what I understand, it makes your ride over the bridge more comfortable.
0:17:00 > 0:17:03- Exactly how, I need to find out.- OK.
0:17:03 > 0:17:05- So I'm hopping in.- Right.
0:17:10 > 0:17:16Even though Brunel didn't complete this bridge, this saddle, as conceived in his original design,
0:17:16 > 0:17:20was essential to making this pioneering structure work.
0:17:20 > 0:17:22So, David, what exactly is a saddle?
0:17:22 > 0:17:25This saddle is an enormous piece of metal.
0:17:25 > 0:17:28It's a combination of cast-iron and wrought-iron plates,
0:17:28 > 0:17:30all bolted together.
0:17:30 > 0:17:34Sits on top of the tower and it connects the chains which come up
0:17:34 > 0:17:38across the gorge with these chains which come up from the anchorages
0:17:38 > 0:17:42and all the weight of the bridge and all the traffic loads on the bridge,
0:17:42 > 0:17:49they're all transferred up the chains to this saddle and it all bears down on the top of the masonry towers.
0:17:49 > 0:17:52This thing's got to cope with forces from different directions.
0:17:52 > 0:17:54How does it manage to do that?
0:17:54 > 0:17:58It's an ingenious method whereby the whole thing sits on a bed of rollers.
0:17:58 > 0:18:01That allows the saddle to move towards the river or away from the
0:18:01 > 0:18:04river depending on the tension in the chains.
0:18:04 > 0:18:11For example, if more traffic comes onto the bridge, that increases the tension in the chains on that side.
0:18:11 > 0:18:16It pulls the saddle that way until the tension in these chains is increased so that they're balanced.
0:18:16 > 0:18:19It's a very clever solution. Was it always part of Brunel's design?
0:18:19 > 0:18:21It was very much part of his design.
0:18:21 > 0:18:31These saddles, along with some of the chains, were in use before they came here, on one of his earlier bridges,
0:18:31 > 0:18:35being the Hungerford Bridge across the River Thames in London.
0:18:35 > 0:18:40And all of the rollers, the base plates, it all came from that bridge.
0:18:46 > 0:18:48Things are looking a bit brighter now, Lu.
0:18:48 > 0:18:50We have a break in the weather, finally.
0:18:50 > 0:18:53That was really grim, but hey...
0:18:53 > 0:18:56Let's have a look at how this thing's held up, shall we?
0:18:56 > 0:18:58- Yeah.- These chains.
0:18:58 > 0:19:02This is probably the smallest climb we're going to do in the whole series.
0:19:02 > 0:19:04Is it?
0:19:04 > 0:19:07But it's going to be fun cos we're going to be sitting right on top of the chains.
0:19:07 > 0:19:11I've found, actually, that the shortest climbs can be the most technically difficult.
0:19:11 > 0:19:20Yeah. So we've got to sort of sidelong our way across a little ledge and then get on to the chains.
0:19:20 > 0:19:22All right.
0:19:22 > 0:19:24OK.
0:19:24 > 0:19:30This couple of feet looks quite perilous, because beneath it are about 300 more.
0:19:33 > 0:19:37Lu, that had better not be skiddy after the rain, or else you're on a ski-slope, girl.
0:19:37 > 0:19:40It's dried off surprisingly well.
0:19:40 > 0:19:42What's it like, Lucy?
0:19:42 > 0:19:43It's cool.
0:19:43 > 0:19:46I'm on top of the suspension bridge.
0:19:46 > 0:19:48This is amazing.
0:19:53 > 0:19:55Lu, my handholds are here.
0:19:55 > 0:19:59Yeah, big handholds and you're just traversing along.
0:19:59 > 0:20:01Well done.
0:20:02 > 0:20:06When you feel comfortable, you can grab the chain.
0:20:06 > 0:20:11- Not sure "comfortable" is the word. - See those gaps in the chain - you can stand on those.
0:20:11 > 0:20:16Brilliant. You can come down here if you want or just stay up there.
0:20:16 > 0:20:18Wherever you feel comfortable.
0:20:19 > 0:20:21There's a place for a picnic.
0:20:24 > 0:20:26It's great to see this.
0:20:26 > 0:20:30You don't get this close up to the real structure.
0:20:30 > 0:20:32It's an incredible sweep, isn't it?
0:20:32 > 0:20:36Yes, beautiful, it's a great, sweeping, beautiful thing.
0:20:36 > 0:20:41It's amazing how this long after it was dreamt up, it still seems an amazing achievement.
0:20:42 > 0:20:46The story of these iron chains is ironic in itself.
0:20:46 > 0:20:51Brunel designed the bridge to have two parallel layers of them and they were manufactured,
0:20:51 > 0:20:58but when the work ground to a halt on this Clifton Bridge in 1843, then they were taken to another
0:20:58 > 0:21:05bridge at Saltash, the Royal Albert, used to link Devon to Cornwall on Brunel's Great Western Railway.
0:21:05 > 0:21:14In 1863, after 20 years of inaction on this bridge, the timber rose and new iron was sought and the new
0:21:14 > 0:21:18engineers, Hawkshaw and Barlow,
0:21:18 > 0:21:23sourced it from London, in fact from another Brunel bridge, Hungerford.
0:21:23 > 0:21:25They brought it on, guess what,
0:21:25 > 0:21:30Brunel's Great Western Railway to Bristol Temple Meads and then to site.
0:21:30 > 0:21:36Isn't it remarkable it was not only brought from another Brunel bridge, but carried on Brunel's railway.
0:21:36 > 0:21:41He carried on supplying this site with what it needed, even beyond his death.
0:21:41 > 0:21:43That's remarkable.
0:21:49 > 0:21:53- How are you feeling up here, Jonathan?- I'm really exhilarated.
0:21:53 > 0:21:59- Are you?- Yeah. - Did you know that this is the highest point we've been to so far?
0:21:59 > 0:22:06- Is it? I didn't know that. - Down to the high-water mark we're at about 320 ft here.
0:22:06 > 0:22:10It doesn't quite feel that high until you start to look horizontally
0:22:10 > 0:22:14and this is what I think is so fabulous, because you just see blue hills beyond you.
0:22:14 > 0:22:17You look over an entire city.
0:22:17 > 0:22:19It's such a wonderful vantage point.
0:22:21 > 0:22:26And now, it's time for us to abseil down.
0:22:28 > 0:22:30Shall we go?
0:22:34 > 0:22:36Make the most of it while you can.
0:22:50 > 0:22:55In 1998, this new mechanical gantry was hoisted up from the river and installed.
0:22:55 > 0:22:59It allows for maintenance to be carried out to the underside of the bridge.
0:23:00 > 0:23:03Lucy and I are making our way down here so that we
0:23:03 > 0:23:07can climb out and get a good look beneath this marvel of engineering.
0:23:08 > 0:23:13This is...not scary.
0:23:14 > 0:23:17It's a good broad base from which to work on.
0:23:17 > 0:23:20What are we going to do?
0:23:20 > 0:23:27We've got this Tyrolean set-up, so we're or Tyrolean-ing.
0:23:27 > 0:23:29That's easy for you to say.
0:23:29 > 0:23:31Across this...
0:23:31 > 0:23:33quite long drop.
0:23:33 > 0:23:36And getting a very close view of the underside of the bridge.
0:23:36 > 0:23:39You can really see the depth from under here.
0:23:39 > 0:23:41Absolutely.
0:23:41 > 0:23:47Then we're going to be abseiling basically straight down this cliff-face
0:23:47 > 0:23:49- on top of the road.- Are we?
0:23:49 > 0:23:55I think this is going to be quite a test for you, for both of us.
0:23:55 > 0:23:57It feels like we're in the mountains.
0:23:57 > 0:24:00I've got a mountain sense of doom.
0:24:00 > 0:24:01What do I do?
0:24:01 > 0:24:04Just clamber over the edge?
0:24:04 > 0:24:09You can lower yourself down on to the ledge that's down here.
0:24:14 > 0:24:18All right, are you ready? 3, 2, 1.
0:24:18 > 0:24:20Whoo!
0:24:22 > 0:24:24- Wow!- A beautiful thing.
0:24:24 > 0:24:26That's a beautiful thing.
0:24:26 > 0:24:28Oh, wow.
0:24:30 > 0:24:38It's an audacious thing, this bridge, I have to say, when you're looking at the drop we have below us.
0:24:44 > 0:24:45You can see here
0:24:45 > 0:24:49the whole of the underside of the bridge and it's rather a more
0:24:49 > 0:24:51complex structure than meets the eye.
0:24:51 > 0:24:56It looks very thin when you see the bridge from a distance but in fact,
0:24:56 > 0:24:59you've got several layers of construction.
0:24:59 > 0:25:04You have first the longitudinal girders - there's one running right above me that goes the whole length
0:25:04 > 0:25:12of the bridge and that is what the rods are attached to, which are in turn carried by the chains.
0:25:12 > 0:25:15That is the primary, suspended element.
0:25:15 > 0:25:23From the longitudinal girders come these trusses, the beautiful lattice work things which curve at each end.
0:25:23 > 0:25:27It's these which carry the basis of the deck.
0:25:27 > 0:25:30The timber deck is held by those ultimately.
0:25:30 > 0:25:37All of this timberwork looks fairly new and in fact it was replaced about 50 years ago.
0:25:37 > 0:25:41The Victorian bridge similarly had a timber deck, but
0:25:41 > 0:25:45when you think about the vehicles in the Victorian age, horses,
0:25:45 > 0:25:51their legacy was leaving manure on the bridge, which rotted the timber.
0:25:51 > 0:25:54I hope these are rather more secure.
0:26:03 > 0:26:06We'll go along and we'll get on to the abseil ropes now.
0:26:10 > 0:26:13Shall we descend, Dr Foyle, seeing as we're here?
0:26:13 > 0:26:17- Shall we, madam?- Let's do it. - Together, you and I.- All right.
0:26:20 > 0:26:22That is a view and a half.
0:26:25 > 0:26:29That actually brings home the audacity of taking on
0:26:29 > 0:26:32- a project like this.- It does.
0:26:32 > 0:26:34Think of a factory full of that ironwork.
0:26:34 > 0:26:37It's like, you're going to put it where?
0:26:37 > 0:26:41- 300 ft in the air? Are you crazy? - LUCY GIGGLES
0:26:41 > 0:26:43Totally amazing.
0:26:45 > 0:26:50Wow, look at where we were. It's amazing.
0:27:03 > 0:27:06That I enjoyed. That was great, Lucy.
0:27:06 > 0:27:08That was awesome.
0:27:08 > 0:27:12That was a really unusual view of the Clifton Bridge.
0:27:14 > 0:27:19I really enjoyed that and I'm pleased we fitted the Clifton Suspension Bridge
0:27:19 > 0:27:22into our roll-call of 15 great buildings because although
0:27:22 > 0:27:26some other bridges are bigger, like the Humber or the Severn,
0:27:26 > 0:27:31they're the great-grandchildren of this bridge and the way it gloriously leaps across the
0:27:31 > 0:27:36Avon gorge makes it spectacular in a way that no early bridge is.
0:27:36 > 0:27:38Nothing can compete with this.
0:27:38 > 0:27:41I think it really is one of Britain's great buildings.
0:27:56 > 0:28:00Next time, how the Victorians' express desire for all things Gothic
0:28:00 > 0:28:04lead to Britain's most spectacular railway station, St Pancras.
0:28:22 > 0:28:24Subtitles by Red Bee Media Ltd
0:28:24 > 0:28:27E-mail subtitling@bbc.co.uk