Fresh wooden posts have been added to ancient holes to recreate a primitive henge clock.

Once one of the world's great cities, Cahokia was a place of religious worship, trade and mass human sacrifice before being mysteriously abandoned.

Less a museum than a bizarre fantasy world created by artists and engineers.

A historic house in St. Louis was plagued by a series of suicides committed by family members involved in a successful brewery.

A museum dedicated to man's boldest venture.

Nature's biggest mammal swims in landlocked Oklahoma.

Collection of skeletal systems from the "world's leading supplier of osteological specimens."

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

The old Route 66 town straddling Texas and New Mexico died along with the Main Street of America.

This fast-food outlet is the only space and UFO-themed McDonalds in the world.

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

The outcropping is graffitied with the name of the beloved musical Muppet television series.

In Tucson a giant metal snake helps pedestrians cross a busy highway.

A wild west cemetery in Tombstone, Arizona, provides a window into the Old West.

An old saloon in the West filled with history, and according to some, a few dozen ghosts.

What is the Thing?

A geological mystery on Camelback Mountain.

This memorial pyramid marker honors one of the United States Government's first official camel riders.

This immigrant bridge once spanned the Thames but is now a fixture of an Arizona city.

All of the 20 occupied houses in this mostly abandoned town feature some curious display of junk art.

Preserving the remains of Native American cultures which otherwise would have been submerged behind Hoover Dam.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

Settled by the Church of Jesus Christ of Latter-day Saints in 1859, this abandoned frontier town has appeared in several films.

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