The world's longest known cave system.

A much more welcome kind of snowbird vacationer, manatees camp out in these springs every winter.

The ghostly remains of an accidental sea.

A museum and shop on Bourbon Street located in the French Quarter.

A semi-scholarly approach to sex.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

A toxic ghost town sitting atop a massive coal fire.

A layered tribute to the work of mosaicist Isaiah Zagar.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

A sharp bend in a dramatic river canyon cut through red rocks.

A snapshot of the city's fascinating voodoo culture.

Most-visited and most-photographed slot canyon in the American Southwest.

Rippling sand dunes frozen in the Arizona rock.

Structure built from the skulls of vanquished foes.

The deepest lake in the United States, and once the site of epic destruction that lives on in legends.

The big toe of this towering monument to a Croatian national hero is worn from years of superstitious rubbing.

Formerly Yugoslavia's "forbidden island," this sleepy little city still holds the abandoned remains of military strongholds.

A wunderkammer of gold and silver reliquaries and ancient saintly bones.

This picturesque medieval monastery guards a small trove of historic treasures.

Longest fortress system anywhere in Europe.

This crucial gathering spot along the "hippie trail" still displays old notes between traveling beatniks and backpackers.

Legend says if you stick your thumb in the hole and it gets wet, your wish will be granted.

A marvel of Byzantine engineering under the streets of Istanbul.