World's first "penitentiary," meant to be humane, drove men insane.

An eerie, decaying ghost town destined to fade into the forest.

The only place for a truly presidential dram.

The world's oldest continuously operating airport was founded by the Wright Brothers.

The last of nine massive kilns that produced many of the red bricks for buildings in Washington, D.C. and northern Virginia in the early 20th century.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

The final resting place of an unidentified revolutionary soldier sits behind a Virginia church.

A former major munitions plant that has been converted into a sprawling art space.

The United States Capitol's former columns still stand.

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

Home to a vast and influential collection of Shakespeareana.

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

This lovely pocket park is one of the most under appreciated in D.C.

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

The "lovely red Vega" of the legendary record-settling pilot.

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

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

The oldest continuously operating fish market in the United States.

Washington's iconic carousel has a nice piece of Civil Rights history.

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

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

The only Leonardo Da Vinci painting in the Western Hemisphere.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.