A wondrous old library overlooking the nation's capital.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

A historic ruin just 20 feet away from a busy highway onramp.

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

A portal into the bricked up canal that runs through the heart of Washington D.C.

A derelict bit of transportation infrastructure hidden in the woods.

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.

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.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

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

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

A painfully obvious spy house sits right across the street from the Russian Embassy.

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

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

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

This beautiful building in the heart of Manhattan's Financial District was empty for decades.

The mysterious image is believed to show Edward Hyde, 3rd Earl of Clarendon, in a beautiful blue dress.