Every drop of D.C. tap water flows through this old waterworks.

The famous abolitionist’s preserved estate is one of Washington's finest monuments to its great Black citizens.

A derelict bit of transportation infrastructure hidden in the woods.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

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

There's an old indoor swimming pool hidden directly underneath the White House Press Briefing Room.

The first presidential bomb shelter was located in an old vault under the Treasury, connected to the White House via tunnel.

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

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.