On and under Britain's spectacular Clifton Suspension Bridge

The Clifton Suspension Bridge spans the River Avon in Bristol, southwest England. Completed in 1864, 110 years after a bridge at the site was first planned, the Clifton still carries cars (for a toll of £1 each way) and pedestrians between the districts of Clifton and Leigh Woods.

The bridge's designer was Isambard Kingdom Brunel, one of Britain's greatest civil engineers. Brunel also designed London's Paddington Station and the SS Great Britain, the first modern ocean liner, which you can tour in Bristol. With his father, Marc Isambard Brunel, he also developed the technology used to dig the first tunnel under the River Thames in London.

The Clifton Bridge's total length is 1,352 feet, but its center span, or the only portion suspended over the river gorge, is 702 feet. The deck is 245 feet above the Avon at high tide, but the surface of the river can drop as much as 42 feet when the tide is out. At 20 feet wide, there's only room for two narrow lanes of traffic and a pedestrian path on either side.

The Clifton Bridge uses wrought iron chains instead of the cables you'd find on a more recent suspension spans like the Golden Gate Bridge. 

The chains, which hang from the towers, then support the weight of the roadway through iron suspension rods that connect the two.

Both the towers and the piers that make up their foundations are composed of local stone. Brunel had meant for the Clifton's towers to be built in an Egyptian-inspired design with sphinxes on top, but they were left with unfinished faces instead to save costs. Though the two towers are the same height (72 feet) their shapes at the top are slightly different.

The steep banks of the Avon River gorge wind toward the River Severn and the Atlantic Ocean. Fun fact: This River Avon is not the same Avon that flows through William Shakespeare's hometown, Stratford-upon-Avon (it's actually one of eight Avons in the UK). And if that wasn't confusing enough, "Avon" is the Celtic word for river.

The southern bank of the gorge is heavily wooded. Peer between the trees and catch a glimpse of some gorgeous homes with views of a lifetime.

The bridge is gorgeously lit at night.

A highlight of our tour are underground vaults beneath the Leigh Woods tower. Built into the tower's abutment during construction, they were covered up when the bridge was completed and not rediscovered until 2002 during a roadway repaving project.

To reach the vaults, you first have to walk down a path near the visitor center until you reach the edge of the gorge.

Then, climb down a ladder that leads to the base of the Leigh Woods Tower.

The ceiling inside the main vault was 40 feet over our heads. Water dripping through cracks in the ceiling since the bridge was finished has formed a forest of thin stalactites made of calcium.

The stalactites are hollow making them incredibly fragile. If I could have reached high enough, I could have broken one easily.

Like in a natural cave, the seeping water also makes stalagmites on the floor of the chambers. These don't get very high, however.

The debris piled against the wall on the left side of the photos was dumped there during the bridge's construction as crews dug the foundation for the pier. 

We had to duck through a short tunnel to access the next chamber.

Stalactites hung from the ceiling of this chamber, as well. Our guide said that when a stalactite becomes too heavy, it will fall to the ground. Luckily none fell during our visit even though we were wearing hardhats. 

Seeping water caused the black sections on the walls.

Tunnels, too small to crawl through, lead to other chambers.