View the ancient remains of buildings and the ancient "River of Hades" before hopping on a train.

Gladiators once walked this ancient, subterranean passage.

This small 16th-century church in Athens is almost entirely surrounded by a modern building.

Legend says this sacred tree was a gift from goddess Athena.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

A freedman baker’s lavish tomb has a relief showing various stages of Roman bread making.

A colossal aqueduct from the second century B.C., deeply hidden in a gorge on the outskirts of Rome.

This is the oldest Roman-made bridge in the city still existing in its original state.

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

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

2300-year-old Roman road connecting the empire.

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

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

The underground sanctuary of a mysterious ancient cult.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

An alchemist's "magic door" stands in the middle of a Roman park.

The yawning maw of this pagan visage is said to bite off the hands of liars.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

The very center of Paris is surrounded by a bevy of strange good luck rituals.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

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

In 2010, Nicolas Cage purchased two plots in this cemetery using one to construct this strange pyramid mausoleum.