America's first federal monument.

Between 1930 and 1946, a tobacco farmer laid his beloved horses and mules to rest in this small patch of pine forest.

This giant iron playfully pays tribute to an early 20th-century architectural trend.

A rare example of a rural school in Washington, D.C.

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

The school tested mustard gas for the U.S. Army during World War I.

The 28,000-year-old specimen is remarkably intact.

Daily lunch spot for many of Washington, D.C.'s cab drivers.

There’s a special club house at the top for the bell ringers.

A historic arena where the Beatles played their first concert in the U.S.

Where the U.S. government kept its actual treasure, before Fort Knox.

A celebrity from the late Cretaceous period.

A Civil War fort in the middle of Washington, D.C. has been swallowed by a forest.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

A massive, majestic mammal watches over pedestrians from his perch atop a former B.P.O.E. lodge.

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

A museum dedicated exclusively to aircraft used in the military.