The tunnel under the Capitol Building where Congress takes out its trash.

The Pentagon is so large that it was planned like a city, complete with internal highway infrastructure.

During WWII the U.S. Navy conducted primitive drone strikes on this Lake Michigan lighthouse.

This nine-story building is the oldest standing skyscraper in D.C.

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

An Industrial Revolution-era public work that purified water using nothing but sand.

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

When it comes to handsignals (and colonialism) rock always beats scissors.

The only tennis court that falls under the jurisdiction of the central bank.

Right next to departures—how convenient!

The Pentagon sits on a former island that was in Virginia at low tide and D.C. at high tide.

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

Chicago's Navy Pier on Lake Michigan was a training hub for aircraft carrier pilots during WWII.

This lovely picnic spot featuring thunderous jet landings is an aircraft spotter’s dream.

The U.S. Air Force has an anti-satellite laser weapon.

A rare wayfinding portmanteau of “Street” and “Avenue.”

The U.S. Supreme Court's secret Cold War relocation facility in the mountains of North Carolina.

Rumor has it the hot dog stand was targeted by two Russian nuclear missiles.

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

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

The U.S. Fish Commission’s effort to mass produce carp.

A derelict bit of transportation infrastructure hidden in the woods.

A historic estate packed with George Washington's heirlooms, and its own nuclear bunker.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.