A spring-fed pool so deep it's used for scuba diving as well as swimming.

The Grand Canyon of Texas.

Just a few miles from downtown Atlanta is a trail covered in a crazy collection of outsider art.

A hospital closed seemingly in the middle of operations, leaving behind fodder for horror films and ghost hunters.

Underground tunnels remain beneath this abandoned mental asylum.

A lesser-known part of the Kinsey Institute is this impressive collection of art, artifacts, and material culture related to human sexuality.

This library and museum is dedicated to the life and literature of the Indianapolis native author.

A flamboyantly decorated bridge signals diversity and fellowship at the entry to Indianapolis' Broad Ripple Village.

These ancient ritual mounds are our best window into the culture of the ancient Mississippians.

A clear blue swimming hole with hidden caves, still unexplored.

An earthwork sculpture built by Robert Smithson in the Great Salt Lake only reemerges during drought.

An entire town preserved as a historic landmark.

A ghost town that held steady longer than most, but finally gave up the ghost.

The first declared National Monument in the United States.

Thanks to a loophole in property ownership, this alleyway has become a cacophonous street gallery.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

An 18th-century Spanish watchtower made entirely of seashell and concrete.

One of the only Florida forts to remain in the hands of the Union all through the Civil War still stands as a historic stronghold.

Bad farming practices caused this unnatural natural wonder.