Skulls from the plague of 1656 and World War II bombings are united by a cult dedicated to caring for the ancient dead.

In a city that boasts four separate inclined cable railways, this is one of the busiest funicular lines in the world.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

These "anatomical machines" are only one of the many strange items in this Italian crypt.

The once forbidden "secret cabinet" of erotic art from excavations of Pompeii and Herculaneum.

An underground paleo-Christian burial site composed of the remains of several cemeteries and Basilicas.

This modern museum of Mediterranean culture is surrounded by a surreal concrete honeycomb.

A cave dwelling that was started by the Celts, expanded by monks, and finished by knights.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.

A natural arch carved by a river gave its name to the so-called "Cave of Forgotten Dreams."

A chapel on a volcanic core, marking the end of a successful journey.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

Lyon, France is home to two remarkably preserved Roman theaters, one dating back to 15 BCE.

This church looks more like a spaceship than a house of worship.

An architectural oddity of six stories, accessed by graceful ramps.

Romania's triumphal arch looks out over Bucharest.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

This giant middle finger statue sends an unambiguous message to Italy's bankers.

A turn of the century building boasting some of the most beautiful art nouveau architecture in Prague.

Looming communist pillar with a Czech twist.

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

Two stunning 17th-century libraries and a cabinet of curiosities.

Macabre astrological automaton clock dating to the late 1400s.

Giant WWII fortresses that fired 8,000 rounds a minute, now home to thousands of pigeons.