A whimsical village of unique treehouses resides in a Washington forest.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

This lab's maddening silence is good for business but bad for sanity.

At this Denver landmark, the meals are compulsory, the sopapillas are complimentary, and the insanity is everywhere.

Panorama exhibition hall in old silent theater with a beautiful backyard garden.

These eerie outliers of the lightning bug family glow a mysterious blue color.

The curiosities and wonders of pharmacy in a delightful historic building.

Scores of vintage street lamps shine along L.A.’s Miracle Mile.

It's not hard to see why the historic Peabody Conservatory of Music's library has been described as a "cathedral of books."

The scuba diving training facility was named for the steam that rises from the cave's chimney.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

This natural wonder drops 16 stories straight down through rare flora and streaming waterfalls.

A modernist landscape of water and sci-fi concrete.

The largest self-built castle in the U.S., six decades in the making.

This knobby, drooping New Orleans oak is a favorite place both for climbing and for meeting giraffes.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

This naturally-sourced hot spring is now home to a clothing-optional resort.

This frequently-photographed waterfall takes only a short hike to visit.

Hollowed out cedar log tubs set in an ancient towering forest.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.

Where manatees are the snowbird vacationers in these balmy Florida springs.

An underwater city for the dead.

A prohibition-style speakeasy takes up residence in the last Victorian residence in Hollywood.