These Great Lakes sea caves accessible by boat in the summer turn into temples of ice reachable by foot in the winter.

The final resting place of a space program monolith.

A multi-storied adobe complex has been inhabited for more than a thousand years.

The superstar of Cold War nuclear bunkers has been featured in countless films but is now barely operational.

A reproduction of earth's many biomes.

The largest earthwork effigy in the world.

A museum dedicated to the alleged Roswell Incident.

Quite simply the largest tree in the world (by volume).

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

An acoustic anomaly with a mysterious cause.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

The world's longest known cave system.

These delicate buggers are some of the rarest fossils that have bubbled up from the Tar Pits.

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

Take a drunken tour inside the world's largest known geode.

Home to items never before seen by the public.

Stepping away from the glitz of mobsters and casinos to learn about the other history of Vegas.

Ninety feet off the valley floor is an ancient dwelling put under protection of the U.S. government by Teddy Roosevelt.

Paranormal experiences in this hotel's room 217 led Stephen King to write "The Shining."

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

A bizarre house filled with an astounding array of collections.

High on a hill overlooking Los Angeles lives a world famous, high power conical Tesla Coil.

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.