A labyrinthine underworld of tunnels and caverns hides beneath the city.

There's a labyrinth of medieval chambers hidden deep below a 15th-century pub.

The oldest inn in England served brew to the crusaders.

A striking 500-year-old mansion provides an unexpectedly sublime home for live deer and a menagerie of exotic stuffed animals.

In this medieval fish bowl, the carp weren't pets.

The ancestral home of beloved English poet Lord Byron has a bizarre history.

The storied English village that pretended to be insane inspired NYC's nickname and the fictional namesake in the DC Comics universe.

This romantic, decaying 13th-century ruin on the edge of Sherwood Forest is reputedly one of England's most haunted places.

Partially collapsed lava tube and cave system complete with concert hall, underground pond, and unique albino crabs.

Below a historic English market town lies a secret underground city complete with kitchens, laundries, storerooms, and an underground lake.

England's foremost purveyor of funeral furniture hasn't changed a bit since the 1960s.

An ancient woodland that inspired a young J.R.R. Tolkien.

A small cell adjacent to this church was once the bedroom for a renowned saint.

More sculpture than building, this architecturally significant temple was built on the spot of Saint Peter's crucifixion.

This hidden alley near the location of Rome's first theater was the site of a curious miracle.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

Among the busts of heroes of the Roman Republic of 1849, there is also a statue of a boy and his dog.

At the crypt of St. Mary of Eulogies and the Dead you are left alone to ponder mortality among piles of skulls.

This basilica is dedicated to two saints, one of which is known more for his famous quote.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

The Vatican's secret porn-festooned bathroom was painted in erotic murals by one of the greatest artists of the Renaissance.

A hidden workshop for creating and restoring Papal mosaic masterpieces.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

If you want to talk to the Pope you will have to stare down this surreal vision of Jesus rising from a nuclear hell.