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.

Possibly the oldest of Britain's ancient henges is also one of its most stark.

Two ancient Buddhist temples crown this dramatic rocky pinnacle.

Isolated atop this Balinese sea crag is a lovely Hindu temple that is said to be guarded by sea snakes.

A solitary tree has grown up all alone on Lake Wānaka, backdropped by the beautiful Southern Alps.

This isolated structure beckons adventurers with sublime views of the Faroe Islands.

Life in this isolated, hilltop lighthouse was lonely, but it sure was lovely.

This bell tower is the only one of its kind in the Netherlands and was a symbol of prestige.

This modern monument to pagan belief looks like it was transported straight from ancient times.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

A century-old cabin off of Highway 30 touts an unusual construction material: dinosaur bones.

The mysterious, fantastical woodland inspiration for "The Lord of the Rings."

This eye-popping Icelandic crater lake is surrounded by red volcanic rock.

The remains of a magnificent medieval fortress that was the capital of a vast empire.

An isolated 17th-century chapel on a remarkable site once dedicated to Celtic sun worship.

The tallest waterfall in the Judean Desert is named for its connection to a biblical figure.

The last remaining predreadnought battleship in the world has been a museum for nearly a century.

A tunnel with windows, so you don't miss out on the impressive views.

The one-time watch house for incoming ships at the Golden Gate now stands abandoned and hidden in trees.

One of the most well-preserved castles in Italy also contains a rare medieval example of a port fortification.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

Ninety feet off the valley floor is an ancient dwelling put under protection of the U.S. government by Teddy Roosevelt.

On the Oregon coast there is a natural hole that seems to be draining the sea.