The narrowest house in America is seven feet of pure spite.

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

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

The oldest continuously operating fish market in the United States.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

This nine-story building is the oldest standing skyscraper in D.C.

D.C. once had its own tiny rival to the New York Stock Exchange.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

A replica of the famous memorial statue at the Normandy American Cemetery hides in an office building in downtown D.C.

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

The house where John Wilkes Booth conspired with his co-conspirators.

Go take a picture with the inventor of the daguerreotype photographic process.

This unassuming passageway played a key role in one of the most important events in U.S. history.

Was there a small "backpack nuke" hidden in the attic? JFK apparently thought so.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

Once the supplier for noteworthy projects like the National Cathedral, this old brickworks now lies abandoned.

The United States Capitol's former columns still stand.

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

Home to items never before seen by the public.

A human attendant once directed car traffic from this structure before automated stoplights.

This petite park lets visitors see and touch examples of fossilized dinosaur tracks.

This castle constructed in 1928 was crafted from drawings of Lismore Castle in Ireland.

This hotel was the site of major events in sports and radio history. It was also used as a detention center during World War II.

One of the now-less-hidden floral gems of the "Emerald Necklace."