This triumphal 16th-century arched gateway leads to the oldest street in Palermo.

This Arabesque Italian castle was built with a primitive, if ingenious, air-conditioning system.

Every inch of this chapel is covered in craftsmanship from across the world.

Behind medieval walls in a corner of bustling Palermo is a breathtaking former mosque once inhabited by a wolf-taming hermit.

Haunting graffiti left by prisoners of the Spanish Inquisition.

This mosaic-lined medieval church was built by the world's first admiral and still holds mass in ancient Greek.

Water and windows define this defensive Italian well.

This picturesque Umbrian city has a subterranean side that has long remained hidden.

This medieval city gate is now a blend of the past and the modern world.

Pompeii's less famous neighbor is still revealing her secrets.

A medieval wash house where people washed clothes in a river allegedly formed by the tears of a mourning nymph.

Long-abandoned art nouveau baths beneath Milan's Piazza Oberdan.

Massive puppet-automaton machines created by French artist collective Machines de l’Ile.

The world's largest reflecting pool is just two centimeters deep.

This plaza is home to a number of works, including Montpellier‘s own Arc de Triomphe.

An Orthodox church built by the Royal Family for the Russian community exiled to the French Riviera.

A medieval military street hidden beneath a charming French fishing village.

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

This historic boathouse was constructed using salvaged lumber from burned barns.

Before Metro, Washington had a robust streetcar network—and you see the remains of this infrastructure if you know where to look.

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

A wondrous old library overlooking the nation's capital.