The oldest continuously operating fish market in the United States.

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

The U.S. Fish Commission’s effort to mass produce carp.

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

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

A portal into the bricked up canal that runs through the heart of Washington D.C.

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

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

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

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.

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

A historic estate packed with George Washington's heirlooms, and its own nuclear bunker.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

Rumor has it the uncarved lump behind the three famous suffragists is reserved for the first woman president.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

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

A derelict bit of transportation infrastructure hidden in the woods.

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

Light bulbs, scrap wood, and tinfoil comprise this homemade throne of the gods.

Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.

This leafy estate is worth $18 million and is so grand it has two mailing addresses.