Structure built from the skulls of vanquished foes.

A giant portrait of an ancient king looms over the river.

Stone age urban planning.

This 14th century castle withstood years of battle but is now sliding off the hills into the Danube.

This massive concrete sculpture is said to be the heaviest communist monument on Earth.

This ancient theater, restored in the 20th century, lives on as a venue for dramatic and musical performances.

The second-largest Jewish temple in Bulgaria was deserted after World War II, seized by the communist government and then abandoned again.

Ancient serpentine sacrifice holder that has stood the test of time.

This remarkably well-preserved Egyptian plinth is pretty well traveled for a giant piece of stone.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

Monasteries on rock pillars, once accessible only by frayed ropes.

The hallucinogenic center of the ancient world.

This legendary city has been a tourist attraction for centuries.

This exclusive resort has completely covered a tiny Balkan island in a 5-star warren of guest rooms.

A miniature train-ride through Slovenia's largest cave system.

High in the clouds of San Marino sits an ancient tower with some curious prisoner graffiti.

Pilgrimage site for star-crossed lovers.

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

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

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

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

2300-year-old Roman road connecting the empire.

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

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