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

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

A derelict bit of transportation infrastructure hidden in the woods.

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

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

A wondrous old library overlooking the nation's capital.

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

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

Enormous piles of historically significant stones, dumped by Congress in a forest, and abandoned for 60 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.

The United States Capitol's former columns still stand.

The first park built over a freeway is a brutalist masterwork.

A river with some unusual, and occasionally dangerous, habits.

A six-story-tall golden pyramid, surrounded by a moat.

Whimsical sculptures dot a woodland path surrounding their creator's old summer cottage.

The spaceship-like theater, which is still in use, was one of the most popular exhibits at the 1964 New York World's Fair.

The oldest certified bowling alley in the United States is in the basement of this century-old bar.

A place to eat for on-the-run agents and espionage enthusiasts.

An off-the-beaten-path place to literally hang beneath Milwaukee's Holton Street Bridge.

A house and yard adorned with bizarre concrete sculptures in a Milwaukee suburb.

A circus of light and sound forms a sensory ode to an iconic train that will never pass through town again.

Robots, lasers, and whoopee cushions, oh my!

This whimsical sculpture garden is a local treasure.