This elaborate towering structure was once famed for its revolutionary height.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

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

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

Home to items never before seen by the public.

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.

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

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.

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

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

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

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

The most accurate timepiece in the world.

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

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

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

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

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

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

One of the Seven Wonders of the Modern World holds the world's tallest metal staircase.

A 98-room castle in the middle of Toronto that bankrupted a 19th century electricity multimillionaire.

A grand Gothic Revival basilica with stained glass depictions of Montreal's religious history has only one soul resting in its crypt.