This amazing ancient cave was kept secret for seven years to protect it from the public.

Located within one of Israel's most picturesque monasteries is also the country's first meteorological research station.

The ceiling of this cavern is dripping with multicolored marble stalactites.

The ridged layers that make up this river canyon represent Earth's geological history.

The ceiling of Prohodna Cave in northern Bulgaria affords a peek at the sky via two deity-sized-eye-shaped holes.

The beautiful baroque library of the Hapsburg empire.

This off-beat, quirky communism-themed bar isn't afraid to poke fun at its history.

A 19th century artistocrat's mansion, turned into a library, hidden in a modern library.

Budapest's Communist-era statues, banished to the suburbs.

This walkway is so narrow it needs its own light to stop pedestrian traffic jams.

A Jenga-style cylindrical tower of books that appears to go on forever.

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

One of the most exquisite Lycian hilltop citadels in Turkey.

A Lycian city of the dead carved into the hillside of Southern Turkey, complete with startlingly human touches.

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

This arch granting triumphal entrance into Antalya was designed to honor the emperor's visit.

This hunter-gatherer architecture is believed to be the oldest religious complex known.

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

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

This ancient subterranean megalopolis is known for the hot oil traps that were installed above each of its entrances.

A deadly ancient portal to the underworld.

This crumbling medieval basilica once attracted pilgrims by the thousands to collect a miraculous dust that formed above the saint's tomb.

Seven early Christians were sealed into a cave where legend has it they slept unharmed for centuries.

The alleged house of the Virgin Mary is tucked away in a park and nature preserve on Mt. Koressos in Turkey and is holy to both Catholics and Muslims alike.