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.

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

A historic neighborhood church is reborn as a psychedelic arts collective.

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

A wondrous old library overlooking the nation's capital.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

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

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

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