Catacombs turned marketplace.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

Eighty million natural history specimens call this gargantuan museum home.

The metal frame is all that's left of a wicker sculpture which once towered over the M5 motorway.

These precariously placed ruins harken back to a 13th-century castle.

This 19th-century island fort built to protect against an invasion by sea.

Go deep down into the earth to experience the world of Welsh coal miners.

The castle still holds traces of the abandoned Roman fort it was built atop.

A tiny village in Wales claims the name of a noble medieval hound slain for a crime he didn't commit.

The largest of only eight working transporter bridges left in the world.

A 19th-century funicular railway shuttles visitors up this surprising sea cliff to one of the world's largest camera obscuras.

A former fisherman's hut deemed too small for habitation is now a delightful tourist draw.

The longest and tallest aqueduct in Britain can actually be sailed across.

A real-life Professor Snape once taught in this Welsh university building, which students of course nicknamed “Hogwarts.”

A spiral staircase connects the limestone cave with Pembroke Castle, birthplace of King Henry VII.

This Welsh village gave itself a ridiculous name in a publicity stunt a century ahead of its time.

The highest peak in Wales is said to be the final resting place of a giant killed by King Arthur.

A miniature Italianate fantasy village on the coast of Wales and the set of ITC classic "The Prisoner."

This valley of hot springs and boiling mud pots is home to the record-holding "Geysir," which originated the English word.

If a glacial river suddenly diving into a sheer chasm via a dramatic, multi-stage waterfall isn't peak Iceland, it's certainly close.

Iceland's largest lagoon is home to stunning multi-colored icebergs.

Medicinal spa created with the discharge from a geothermal energy plant.

One of the few surviving street funiculars in the world.