A deadly ancient portal to the underworld.

Roman ruins top white travertine terraces formed by ancient hot springs.

This church houses the tomb—but not the remains—of St. Nicholas, the likely progenitor to Santa Claus.

Flames have been burning within this mountain for more than 2,500 years.

These tombs were built into the side of a mountain so that ancient angels could reach the dead.

While not Turkey's deepest underground city, this subterranean redoubt is the largest.

The deepest underground city in Turkey was designed to protect 20,000 people behind massive stone doors.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

A surreal statue honoring Prague's favorite literary son.

Inspired by the Rialto Bridge in Venice, these three clustered bridges were just one part of a Slovenian architect’s grand vision.

Strange rumors surround the artist who created these solemn metal guard dogs.

A whimsical bridge adorned with decorative dragons.

Picturesque basketball courts sheltered by historical defensive walls and with an enviable sea view.

The big toe of this towering monument to a Croatian national hero is worn from years of superstitious rubbing.

Ming Dynasty necropolis raided during the Cultural Revolution.

The most famous location in China was home to whole dynasties worth of imperial rulers.

An ancient fortification lives on in this Chinese city.

A small etching on the white marble parapet was written in runic script by a Viking mercenary.

A marvel of Byzantine engineering under the streets of Istanbul.

Carvings in Turkey's Marble Road may have directed ancient Romans to a hidden brothel.

The ancient latrines of the Greeks, in all their public glory.

These Egyptian statues have survived for 3,400 years and were an acoustic wonder of the ancient world.

Standing atop 2nd-century Roman ruins, this church is one of the oldest and most iconic in Old Cairo.

The large collection of pre-Columbian pottery might make you blush.