This series of Scottish caves has no clear purpose other than baffling historians.

Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

Beneath the impressive baroque cathedral that rises from the center of Berlin lies the largest collection of Prussian royals in the world.

An extensive collection of reliquaries containing the bones of saints housed in the largest Catholic church in Venice.

A sinister pyramid in the Frari contains the heart of the famous neoclassical sculptor.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

Hanging within this medieval church are the bones of a beast allegedly slain by a fourth-century saint.

The tower was originally used as a chimney for the waste incinerator of St. John's Precinct and Market.

This beautiful "lagoon" is actually a toxic soup filled with cars, carcasses, and trash. When warnings couldn't stop people from going for a dip, the town dyed it black.