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

Largest Roman Catholic church in North America.

The house where John Wilkes Booth conspired with his co-conspirators.

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

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

The most accurate timepiece in the world.

Where the U.S. government kept its actual treasure, before Fort Knox.

Decades before the scandal, this staircase on the river was a literal "water gate."

A celebrity from the late Cretaceous period.

The oldest continuously operating fish market in the United States.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

There’s a hidden military meme engraved on the World War II Memorial.

Washington's iconic carousel has a nice piece of Civil Rights history.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

This seemingly out-of-place gas station by the Watergate hotel was once described as the most expensive gas station in the world.

Perhaps the most scandalous statue of America's first president.

Once home to seven different roller coasters, Glen Echo has undergone many transformations since its founding in 1891.

A star fort along the C&O Canal in western Maryland that protected America in three wars.

The tallest The Church of Jesus Christ of Latter-day Saints temple in the world soars above the Beltway.

This rare triple-jurisdiction drawbridge passes through Virginia, Maryland, and Washington, D.C.

FDR's Art Deco hospital tower was hopelessly inefficient.

The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.