An abandoned railroad tunnel is now filled with bioluminescent bugs.

A mechanized clock where a man fights off a dragon, crab, and rooster.

An unusual number plate signifies the building's saucy past.

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

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

Disks are rolled out onto the south lawn to absorb the impact of Marine One's wheels like giant coffee coasters.

A surprising, but overlooked example of geology in the middle of the nation’s capital.

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

An 18-mile-long tunnel for sewage waste will soon wind within the bowels of Washington, D.C.

This unassuming passageway played a key role in one of the most important events in U.S. history.

Amid the sprawling Defense Intelligence Agency Headquarters is one of Washington's least accessible museums.

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

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

Sit where JFK proposed to Jackie or where Nixon dined on meatloaf at this storied pub.

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

100 years later, they're still down there.

Washington's top-secret Cold War-era doomsday communications tower is located in a small neighborhood park.

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

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

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

Before Nixon, "watergate" meant canals.

This robust fence in front of a historic Georgetown home is likely made from hundreds of recycled Revolutionary War firearms.