A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

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

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

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

This robust fence in front of a historic Georgetown home is likely made from hundreds of recycled Revolutionary War firearms.

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

The span is crooked and made from two older recycled bridges.

The oldest building in the District of Columbia was preserved because of a mistaken connection to George Washington.

The towering figures were created from the cemetery's fallen old-growth trees.

An overlooked oasis of quiet on the grounds of Washington's monumental basilica.

A clone of a cloned tree that was so important it allegedly had its own guards.

A small triangle of DC grass is the final resting place of one of Sonny and Cher's songs.

These recently uncovered walls are all that's left of Washington, D.C's first defense contractor.

A historic ruin just 20 feet away from a busy highway onramp.

A hoard of sky catalogs, astrophysical journals, even the works of Galileo and Copernicus.

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

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

When it opened during the final years of the embargo, all the drinks and cigars were free.

People escaping slavery may have hidden inside a corpse vault.

A Spiritualist house of worship where believers communicate with the dead in the spirit world.

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

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

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.

A derelict bit of transportation infrastructure hidden in the woods.