This fantastical waterfall is hidden in a cave located in a cracked cliff.

If a glacial river suddenly diving into a sheer chasm via a dramatic, multi-stage waterfall isn't peak Iceland, it's certainly close.

This valley of hot springs and boiling mud pots is home to the record-holding "Geysir," which originated the English word.

Surrounded by ash fields in Iceland, an impossibly verdant valley looks like something out of a fairytale.

Be(w)ar(e) the moat around this historic Czech castle.

The U.S. government built the million-pound stack of steel during the Space Race.

The now-overgrown beach resort was once frequented by Yugoslav military elite.

A marvel of Byzantine engineering under the streets of Istanbul.

This massive subterranean fissure is known as the "underground Grand Canyon."

Yugoslavia's biggest underground airport lies in ruins.

In the town of Třeboň, carp is king.

A church of bones, decorated with 40,000 human skeletons.

Macabre astrological automaton clock dating to the late 1400s.

Looming communist pillar with a Czech twist.

Bridge that died in war and was resurected.

Gargoyle head that brings good luck.

This one-time health resort was used by aristocrats around the world.

A whimsical bridge adorned with decorative dragons.

Ancient serpentine sacrifice holder that has stood the test of time.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

This remarkably well-preserved Egyptian plinth is pretty well traveled for a giant piece of stone.

This decrepit abandoned building is made all the more eerie by its dark history.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

The ghostly remains of an accidental sea.