The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.

A house carved into a rock in the 1940s.

One of the world's oldest and most massive living organisms is a grove of quaking aspens.

This geothermal hot spring hides beneath a slowly growing mineral dome.

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.

Here, at the "world's longest art gallery," you'll find forty miles of ancient petroglyphs and pictographs.

A 24-hour vending machine restocked daily with homemade full-sized pecan pies.

A gorgeous garden oasis with winding paths, stone bridges, and a troubling history.

A Victorian mansion, painstakingly reproduced to appear just as the the Munster's family home did on TV.

A medieval castle in the middle of rural Texas.

The Grand Canyon of Texas.

A taste of Middle Earth, in the middle of the Bayou City.

Home to the largest urban bat colony in North America, estimated at 1.5 million bats.

A sculpture made of 10 Cadillacs as a monument to the "Golden Age" of the American automobile.

A modernist landscape of water and sci-fi concrete.

One part antique store, one part curiosities hodge-podge.

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

Continuing the tradition of the dime museum in style.

The mysterious wonder of an underground waterfall is illuminated by multicolored lights.

Wild lights and sound effects turn a walk through some caves into an eye-popping 1960s tourist attraction.

All that's left of the quintessential "cabin in the woods."

Enormous lake at the bottom of a unique cave system.

The ravine where Jesse James supposedly performed an impossible jump to evade capture.

Hidden behind Lincoln's head is a 70-foot-long chamber containing enamel plates documenting American history, sealed in a teakwood box in a titanium vault.