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

Live a night as a Byzantine King, with a minibar and private jacuzzi.

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

Giant reed houses made in the marshes of Southern Iraq.

This vast, water-filled underground labyrinth can only be toured by boat.

One of the oldest scientific gardens in Britain, containing more than 13,302 plant species in its core collection.

A rocky sea serpent hides caves, blowholes, and a spectacular natural bridge.

A island reachable by a causeway at low tide is possibly one of the earliest Western European locations to be identified in text.

Sometimes an island, sometimes a rocky outcropping connected to the world by a tiny suspension bridge.

Twice a day this ancient path disappears with the tides, leaving the Holy Island of Lindisfarne out to sea.

At the center of an island in the middle of the Indian Ocean is a deep chasm ringed by tall waterfalls.

Fabulous formations, weird and wonderful wildlife.

This picturesque island graveyard is the final resting place of dozens of notorious pirates.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

This former limestone quarry is now a subterranean wonderland of grand stonework.

This irregularly shaped sea fortress has defended not one but three different sovereign states.

Something's missing between the arcades of the Palazzo della Ragione in "the city of the three withouts."

The oldest botanical garden in the world that technically isn't the oldest.

The final resting place for the remains of 143 Habsburg royalty.

A tropical paradise just a short trip from the opera house is filled with beautiful winged creatures.

Baroque celebration of the end of the Great Plague of Vienna.

This African beach is home to thousands of rare mainland penguins that are known for their annoying voice.

A tiny, hidden alleyway dedicated to the father of meteorology.

A Victorian Gothic masterpiece housing a world-class collection of rare books and manuscripts.