The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

Home to a vast and influential collection of Shakespeareana.

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 oldest continuously operating fish market in the United States.

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

A gift from Japan, 17th-century lantern stands among the cherry trees at D.C.'s Tidal Basin.

An overlooked memorial honoring the local Washington residents who died in World War I.

Decades before the scandal, this staircase on the river was a literal "water gate."

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

The only tennis court that falls under the jurisdiction of the central bank.

A "Bugseum" dedicated to all things insect-related resides behind a pest control company.

An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

This brick-lined pedestrian walkway was once a railway tunnel used during the Civil War.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

The national park was once a plantation estate.

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

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

The hippo that stands on this university campus was once a drunken flea market purchase.

Garments from across the globe call this hidden gem home.

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

Behind an abandoned storefront is an example of pioneering 1930s gas station architecture.

This bridge over D.C.'s Rock Creek Park is sometimes called the "Buffalo Bridge" because of its four buffalo sculptures, which were cast from a single piece of bronze.

The oldest house in Washington, D.C. wasn't originally constructed in the nation's capital.

A tribute to the pop culture icon overlooks this Washington D.C. intersection.