Natural stone arches form a walkable "cathedral" at low tide, then disappear entirely when the water returns.

Inhospitable caverns just beneath this island paradise offer insights into alien worlds.

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

A massive underwater sinkhole made famous by Jacques Cousteau.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

Stalactites and stalagmites in a beautifully lit cave.

The glowing blue Nymphaeum of Emperor Tiberius.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

The most alien-looking place on Earth.

Coastal dunes, site of buried Egyptian movie set and former utopian colony.

Hidden in the back of a disused small town hotel is a dive bar shellacked with over a million pennies.

A hotel and restaurant serving as the mecca of kitsch.

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

A strange house built only at night, with rumored mystic inspiration.

Two rocks in a perpetual kiss and one of "the most romantic spot in America."

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

Featuring a casually threatening atmosphere along with dessert and coffee to die for.

An extraordinary mixture of natural beauty and man-made phenomena.

A roaring, awe-inspiring double cascade of icy water flows through woodland Oregon like something out of a Tolkien novel.

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

A vertically floating hemlock controls the waves and weather at Crater Lake.

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

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

One small town in the Pacific Northwest transformed itself into a Bavarian-themed tourist destination.