The largest self-built castle in the U.S., six decades in the making.

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

The highest point in Texas is capped by a big silver pyramid.

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

The ghostly remains of an accidental sea.

Once in disrepair, this popular Texas stop along iconic Route 66 has been restored to its past glory.

This Nevada lake holds its titular natural pyramid and, if the legends are true, a number of dangerous spirits.

Beneath a Virginia City bar is the entrance to an abandoned gold mine.

Semi-recognized center of the world, with many oddities.

This abandoned Navy base was transformed into an off-grid alternative living community for thousands of people.

A hand-built folk art installation covered with messages of God's love.

An eatery for UFO seekers on the Extraterrestrial Highway.

The drama of nature in full effect in this Nevada State Park.

Oh, just a motel on the edge of the desert decorated with thousands of clowns conveniently located next to an abandoned graveyard.

San Francisco's urban bison herd has persisted in the face of extinction, development, and disease.

A collection of 20th-century automata, penny arcade games, and musical contraptions.

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

A speakeasy takes on Chicago's drinking culture.

The scene of one of the darkest moments in American labor history has been left essentially untouched since the tragedy.

See six states, pickled freaks, rocks, and antiques.

A small car graveyard sits in the shadow of the famous Cadillac Ranch.

These massive mitts are made of 30 tons of devotional bronze.

A century-old cabin off of Highway 30 touts an unusual construction material: dinosaur bones.

This is one really big nut.