Also known as the Founding Church of Scientology.

An overlooked memorial honoring the local Washington residents who died in World War I.

When it comes to handsignals (and colonialism) rock always beats scissors.

The walls of the iconic dome are hollow and have a secret stairway.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

A wondrous old library overlooking the nation's capital.

A historic neighborhood church is reborn as a psychedelic arts collective.

A working model of the entire San Francisco Bay and much of the Sacramento River Delta, complete with regular tides that change every 14 minutes.

A Mysterious Masonic tomb in San Luis Obispo.

A favorite haunt of dinosaur loving children and hallucinogen loving hippies alike.