A 2000-year-old Roman amphitheater lies just below Guildhall Yard.

This small chapel is built of human bones and decorated with a golden skeleton.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

A rather vulgar example of the transition from Latin to the Italian vernacular.

A Nesting Doll of Churches.

Architectural monsters are devouring this palace's every door and window.

Its interior is adorned with some of the best examples of early Christian mosaics.

This forgotten chalk mine was reopened thanks to a massive effort from the local community.

This longship was a gift to commemorate the 1500th anniversary of the Anglo-Saxons arrival in England.

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

Plaques on its facade commemorate the Tiber's most destructive deluges.

A statue representing a lost Roman profession that was vandalized for centuries.

A massive marble foot is tucked away in a small alley near the Pantheon.

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

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

A forgotten "city of water" underneath the famous Trevi district.

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

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

A collection of objects supposedly singed by the hands of souls in purgatory.

A wonderfully eclectic Victorian aquarium lies in the basement of the Horniman Museum.

A hidden treasure in London with a rich medieval history, and the resting place of many luminaries.

One of the oldest remaining Catholic churches in England is home to the hand of a 7th-century saint.

The world's largest collection of ship figureheads includes figures from legends and history alike, from Sir Lancelot to Abraham Lincoln.