Before Metro, Washington had a robust streetcar network—and you see the remains of this infrastructure if you know where to look.

The site of the climactic scene from the classic horror film is now a historic landmark.

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

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

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

Corn-inthian columns with a uniquely American take on neoclassical architecture.

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.

A nostalgic bibliographic gem.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

Look closely and you’ll notice that the color changes a third of the way up the tower.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

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

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

On the Fourth of July this area will transform into a Pompeii-like storm of falling embers and ash.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

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

The controversial urban planner who designed Washington, D.C., was buried in Maryland, and can presently be found in Virginia.

Soldiers were buried next to Lee's house in the center of Arlington Cemetery to dissuade the general from reclaiming his property after the war.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

The tomb was guarded by soldiers from both sides of the war, and some left their initials carved in the brick.

A diorama of the Civil War, fought by cats.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

The house that Frank Lloyd Wright "(shook) out of his sleeve at will" at the age of 86.