A strange anthropomorphic stele with a mysterious inscription that has never been deciphered.

The verdant mossy ruins of a Franciscan monastery lie in the remote Sintra hills awaiting exploration.

An engineering error ensured this cavernous 350-foot-long subterranean thoroughfare was never used as intended.

Known as the "Finger of God," a dramatic rock formation resembles a divine hand extending towards the heavens.

This isolated island is often capped by its own fluffy cloud.

Once one of the world's great cities, Cahokia was a place of religious worship, trade and mass human sacrifice before being mysteriously abandoned.

The turquoise-studded skull of a long-dead Aztec man sits within Mexico City’s Museum of Anthropology.

This ancient jade mask depicting the Zapotec bat god was found in the ruins of the pyramids of Monte Alban.

This medieval tower is all that remains of the castle where Joan of Arc was held before being burned at the stake.

After visiting hours, this picturesque waterfall is essentially turned "off" to be used for hydroelectric power.

A menacing statue of this mythical creature can be seen at the legendary site of the monster's lair.

The abandoned remains of this once-thriving hotel looms over the city, awaiting an uncertain future.

This unassuming tree stump reportedly traces its roots to the famous pharaoh queen's reign.

The ruins of an abandoned church loom within a picturesque Ukranian village.

Scotland still bears an enormous scar of its Roman past.

This metal tower in the desert provides views of a handful of Nazca geoglyphs.

These layered sandstone mountains in China look like they are made of pressed crayons.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

This vertical pinnacle in China was the inspiration for the floating mountains in the movie “Avatar.”

A magical sinkhole on the Yucatán Peninsula is adorned with mini waterfalls and hanging vines.

Romania's "Red Ravine" is a little-known natural wonder that bears a resemblance to the Grand Canyon.

Raging waters have created a strange geological site that looks like something off of a progressive rock album cover.

Climb down into the largest sinkhole in Qatar.

After millennia of erosion by sand and churning water this Brazilian valley now looks like a lunar fantasy.