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

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

A historic arena where the Beatles played their first concert in the U.S.

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

There’s a special club house at the top for the bell ringers.

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

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

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

Obscure Freemasons still live in D.C.’s largest private residence.

A haunting tribute to pioneering photographer Clover Adams.

Largest Roman Catholic church in North America.

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

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

Fittingly, America's museum of architecture is itself a magnificently designed old building.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

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.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

This grand gothic brewery has been pumping out suds for over a hundred years.

Home to items never before seen by the public.

The site of the climactic scene from the classic horror film is now a historic landmark.

Part of a WWII submarine is lurking outside the Washington Navy Yard parking lot.