The rogue roots are gradually consuming some of the historic marble grave markers.

At 207 feet, one of the world's longest continuous escalators.

Sweet Willy, at 30 feet tall, is the world's biggest beagle.

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.

An overlooked memorial honoring the local Washington residents who died in World War I.

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

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

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

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

The most accurate timepiece in the world.

The oldest continuously operating fish market in the United States.

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

There’s a hidden military meme engraved on the World War II Memorial.

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

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

Home to items never before seen by the public.

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

This Yellowstone geyser may not shoot as high as the nearby Old Faithful, but it erupts for considerably longer.

The only natural lake in the world that drains into both the Atlantic and Pacific Oceans.

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

An architect's childhood fantasy treehouse made real.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

A beautiful geyser under environmental threat.

The first declared National Monument in the United States.