The school tested mustard gas for the U.S. Army during World War I.

The romance of early commercial flight still fills this Art Deco destination.

The United States Capitol's former columns still stand.

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

The remains of a historic plantation nestled in between a parking lot and the rental car return at Reagan National Airport.

A super-sized promotional trick that is now a D.C. landmark.

Right next to departures—how convenient!

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

The privately owned cemetery that holds room for Washington's finest when they step down from life.

A haunting tribute to pioneering photographer Clover Adams.

A clone of a cloned tree that was so important it allegedly had its own guards.

The U.S. Navy’s preposterously detailed mini battleship took 77,000 hours to complete.

One of the largest artillery pieces in the world sits in a Washington D.C. parking lot.

An overlooked oasis of quiet on the grounds of Washington's monumental basilica.

This forgotten boat elevator was an engineering marvel in its heyday.

Part of a WWII submarine is lurking outside the Washington Navy Yard parking lot.

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

A building shaped like the Army Corps of Engineers logo, because why not?

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

The iconic D.C. restaurant where the Cuban Missile Crisis was negotiated, now a Walgreens.

An obscure federal monument honors the French diplomat who served as Ambassador to the U.S. during WWI.

Bar full of oddities, specimens, artifacts and homages to the great dime museums of the past.

The sci-fi villain is a little-known inhabitant of the U.S. capital's largest cathedral.

There’s a special club house at the top for the bell ringers.