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

Local legend says Isaac Newton built this footbridge without any screws, bolts, or nails.

360° views of the city plus five floors of optical illusions and hands-on science.

This extinct volcano rises above Edinburgh and is special for its panoramic views over the city.

One of Ireland's most infamous prisons for rebels including men, women and children.

Dublin's "Dead Zoo" serves as a window to Victorian museum design.

Follow the original medieval paths that wind through this intriguing section of the city.

The National Railway Museum in York is the largest railway museum in the world, attracting almost 1 million visitors per year.

Harry Potter once visited this massive limestone cliff, which was carved by an ancient glacial river.

A modern English garden of eccentric beasts, follies, and oddities.

Although it appears ancient and mysterious, the quirky folly was actually built 200 years ago by an eccentric estate owner.

Where Agatha Christie mysteriously disappeared in 1926.

One of the oldest and certainly best preserved Cistercian abbeys still in existence.

Astonishing rock formations dot the Brimham Moor landscape.

This lovely little burbling creek is actually a deadly waterway that has dragged down everyone who ever set foot in it.

Once thought to be the mysterious work of a witchy prophetess, a well with unusual properties turns objects into "stone".

A 600-year-old mini shrine guarded by a sword-wielding knight hides in a crumbling cliff face.

A bench and a bridge pay tribute to Birmingham's favorite heavy metal band.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

There's a mini version of Iguazu Falls hidden in the Balkans, and it's got a rope swing.

This picturesque monastery at the base of a cliff is a peaceful oasis open to all visitors.

This abandoned airplane hanger is said to have once been a top secret launch facility.

Bridge that died in war and was resurected.

A former bank seized as a sniper vantage point during the Bosnian War is now a secret graffiti art gallery.