The first purpose-built art gallery in the United States is once again open as a center of craft arts.

The oldest continuously operating fish market in the United States.

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

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

The national park was once a plantation estate.

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

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

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

A derelict bit of transportation infrastructure hidden in the woods.

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

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

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

People escaping slavery may have hidden inside a corpse vault.

The winding route passes through an enclosed alleyway, two tunnels, and leads to the White House basement.

Franciscan monks created a facsimile of the Holy Land for North Americans who couldn’t afford the trip overseas.

A secret greenspace hides atop a Capitol parking garage.

A take-out restaurant that only serves cuisine from countries with which the United States is in conflict.

Once the most painted on object in the world, this short campus fence is well on its way to being so again.

The largest university building in the West is a gothic masterpiece containing dozens of theme rooms based on different countries.

A quiet, gothic haven nestled between Pittsburgh's Squirrel Hill and Point Breeze neighborhoods.

This church in Pittsburgh is home to the largest collection of religious relics in North America.

The trials and tribulations of marking Poe's grave.

Crammed into a Baltimore row house is an oddities shop that sells everything from skulls to dead insects.