A popular swimming hole that hides one of America's most deadly diving spots.

This unique structure in suburban Austin is made up entirely of other people's castaways, and constantly changing.

Every week, a festive public jam session breaks out in downtown Asheville.

The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

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

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

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

An artsy hidden staircase leads to breathtaking views of San Francisco.

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

This iconic L.A. bookshop is housed in an abandoned bank—both symbolic and chic.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

A research lab and hands-on museum where visitors can experiment with retro technology.

An absolutely beautiful 200-foot stained glass installation traces the evolution of knowledge.

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

The longest navigable underground river in the United States is home to countless blind and albino animals.

A humble homemade ride attracts visitors from around the globe to this small Midwestern town.

A turn-of-the-century architectural marvel built on healing mineral springs and salt licks.

Taxidermy, Cigar Store Indians, A Model of a New York Tenement and Delicious Draft Root Beer.

More than five miles of underground passageways.

One man's vision and a labor of love of many.

The history of whiskey and all of its boozy glory, from Colonial days to modern American cocktail culture.

Symbolic attempt to overcome the issues of life.

A once-booming Mississippi River town with a history of racial violence is now eerie and mostly abandoned.

Patrick Dougherty's fantastic living tree sculptures, mind-blowing but temporary.