The vast chamber inside this abandoned cooling tower looks like something out of a sci-fi dystopia.

Hanging over one of Japan's "hidden valleys," these vine bridges must be remade every three years.

This simple apartment may have inspired some of the most important theories in the history of science.

A beautiful maze marks where three countries meet.

An Ethiopian "Jerusalem" featuring a church hewn out of a single rock.

This tiny Bulgarian town offers a stunning location in the mountains and a storied history.

The largest prehistoric ruins south of the Sahara, once a powerful center of international trade.

A natural arch carved by a river gave its name to the so-called "Cave of Forgotten Dreams."

Series of underground houses inhabited continuously for centuries.

This huge pile of volcanic boulders hides a stunning network of secret grottoes.

A massive underwater sinkhole made famous by Jacques Cousteau.

This beautifully deceptive waterfall is something far different from what it appears to be.

An emerald-green grotto just a short trip from Austin.

A hidden treasure of an abandoned city lies deep in the jungles of Campeche, Mexico.

A spectacular cave and a beguiling lake.

Every equinox this Maya pyramid puts on a spooky ancient light show.

A hacienda that features all things uniquely Yucatán.

A gallery of underwater art that can be visited by man and fish alike.

An ethereal glowing blue ocean cave in Croatia.

The largest underground church in Europe.

The fairy tale castle of the "fairy-tale king."

This historic island prison holds one of the dungeons from the Count of Monte Cristo even though it is a work of fiction.

A strange house built only at night, with rumored mystic inspiration.