These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

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

A theme park that suffered massive flooding during Katrina was abandoned, and now proves irresistible to trespassing explorers.

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

Dramatic river bend surrounds a natural red-rocked pedestal.

These old stone ruins in the Oregon wilderness were once bathrooms and are steeped in legends of murder.

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

An immersive environment that is part haunted house, part choose-your-own-adventure, and part jungle gym.

A snapshot of the city's fascinating voodoo culture.

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

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

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

A crumbling hospital from the 1850s on Roosevelt Island.

World's first "penitentiary," meant to be humane, drove men insane.

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

Rippling sand dunes frozen in the Arizona rock.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.