Reproductions of nine banned oil paintings coyly hidden behind a curtain in a New Mexico conference room.

A plaque immortalizes the spot where the early American spy said his famous last words: "I only regret that I have but one life to lose for my country."

The ancient necropolis houses the immense rock-cut tombs of four Persian kings.

Charles Babbage's proto-computer, painstakingly brought to life.

This whimsical winery by Antoni Gaudí looks ripped from the pages of a fairytale.

This waterfront museum in Maine is dedicated to the history of the smoked-herring trade.

A half-mile-long stretch of medieval forts built after a devastating pirate attack persists amid the modern port city.

These colorful French islands spent a stint bootlegging booze during American Prohibition.

Hop aboard a charming bog train to explore this rare open-air museum of peat.

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

The palace window through which Protestant nobles flung two Catholic regents, thus sparking the Thirty Years' War.

Italy's third-largest Roman arena gives a peek into the underground operations beneath the ancient spectacles.

135 bronze medallions mark a French meridian line which once rivaled the hotshot Greenwich timeline.

This unattributed sculpture in Amsterdam is hiding in plain sight.

Hundreds of secret cabinets built into the walls of legendary poisoner's private work room.

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.

The "Greatest Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

St. Francesca Romana, patron saint of drivers, resides in the church she founded.

Jesus' footprints and the first catacombs in the world.

One of seven Jewish catacombs in Rome and one of only two open to the public.

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

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

The underground sanctuary of a mysterious ancient cult.