Depending on who you ask, this controversial treehouse is either a charmingly creative child's playhouse or an illegal encroachment on public land.

The privately owned cemetery that holds room for Washington's finest when they step down from life.

A striking memorial to the 21 lives lost in an explosion at the Washington Arsenal

The discovery site of the "Capitalsaurus," the official dinosaur of Washington, D.C.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

A super-sized promotional trick that is now a D.C. landmark.

Part of a WWII submarine is lurking outside the Washington Navy Yard parking lot.

One of the largest artillery pieces in the world sits in a Washington D.C. parking lot.

Outside the Department of Transportation, a collection of artifacts honors the history of how we get around.

Now a living classroom, this house was once the home of Reverend James Clinton Dent, a formerly enslaved man and a pastor.

This statue of one of baseball’s greatest pitchers looks like something out of a sci-fi horror movie.

This lonely waterfront memorial to the men of the Titanic was erected by the "Women of America."

A historic neighborhood church is reborn as a psychedelic arts collective.

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

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

The only National Monument ever to go missing for nearly 50 years then resurface in a dump.

This tree is a living witness to the beginning of the Civil Rights Movement.

This statue is dedicated to Grace Sherwood, the last person in Virginia to be convicted of being a witch.

A whimsical, but often overlooked clock in Park Avenue.

The notorious headquarters of a corrupt political machine.

Scenic mount trashmore, Virginia Beach's most curious waterfront still has a couple of secrets.

Nope, not Washington Irving's house.

This abandoned subway station can still be seen on regular commuter trips.

A posh members-only club with a literally dramatic history.