The secret city built by the Manhattan Project.

Home to items never before seen by the public.

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

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

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

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

The "lovely red Vega" of the legendary record-settling pilot.

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

100 years later, they're still down there.

The institution is sitting on a goldmine of 21,000 paints, varnishes, pigments, and primers preserved for posterity.

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

A nostalgic bibliographic gem.

An unassuming, powerful monument north of the U.S. Capitol bears witness to the resilience of Japanese Americans during a time of grave injustice.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

A little marble compass above George Washington's (empty) tomb in the Capitol marks where D.C.'s four quadrants intersect.

This statue of the "father of television" stands prominently in the United States Capitol.

A promising candidate for the lost rock laid by George Washington was unearthed, but the hunt is still on.

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

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

Corn-inthian columns with a uniquely American take on neoclassical architecture.

Senators used to relax in the nearly forgotten marble tubs now hidden in the U.S. Capitol Building's basement.

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

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