A marvel of Byzantine engineering under the streets of Istanbul.

A gorgeous, Gaudí-esque stairway constructed in the city of Istanbul by a prominent Jewish family.

A sixth-century Byzantine cistern hidden below a modern carpet store.

Giant eggs, walls of bread, and nightmare surreality mark the largest collection of works by Salvador Dalí.

The largest and best-preserved Roman amphitheater in Africa was designed to seat 35,000 people.

The ancient heart of Tunis is an enormous maze of narrow streets and alleyways.

A ghostly mansion in the middle of downtown Tunis.

An ancient Phoenician citadel once stood at the site where Queen Dido first landed, according to legend.

An ancient burial ground believed to have been used for ritual sacrifice.

Mummified monks and the accidentally interred, in a 17th-century crypt.

This hanging crocodile is thought to be the "dragon" that once plagued a Czech city.

A peculiar clock commemorates a historic victory won by ringing the noonday bell an hour early.

Pay your respects to a country that only existed for a few weeks.

This Transylvanian church has changed its denomination four times.

This massive underground salt mine now holds a sci-fi theme park in its depths.

A 13th-century convent where St. Margaret of Hungary spent her teenage years.

This Hungarian castle was built out of cardboard and wood until it proved so popular that it got upgraded to stone.

A diminutive statue that was inspired by the sculptor's own daughter.

This Slovak bridge is known both for its connection to a national uprising and its UFO-shaped eatery.

The blood-soaked ruins of the castle where the murderous Blood Countess was walled in alive.

After 11 years of reconstruction work, Slovakia's finest hilltop chapel complex is finally reopen to the public.

Three bridges and one giant canyon make up this fantastic Spanish settlement.

One of the most spectacular bridges in Spain spans a narrow chasm that divides the city of Ronda.

World's second largest particle accelerator, where nature reveals its secrets.