This rare triple-jurisdiction drawbridge passes through Virginia, Maryland, and Washington, D.C.

The 72-foot giant escaped confinement in a large patch of mulch only to be reburied in the sandy shores of the Potomac River.

A mammoth pair of Civil War artillery guns abandoned out in the forest.

This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

Remains of a historic fountain that was mysteriously lost in the demolition of a D.C. traffic circle.

The ruins of an 18th-century mansion that was once named "Mistake" by the man who had it built.

A state park that once served as an important river crossing, and now offers protected lands for endangered plants and animals.

One of the earliest and best-preserved buildings in Charles County, Maryland.

The remnants of a wooden-hulled fleet built and abandoned in WWI, now home to a thriving ecosystem.

A small and somewhat hidden memorial to 68 local veterans of the Vietnam War.

This marker at the entrance to the Humphreys Engineer Center honors the former Chief of the Army Corps of Engineers.

Dedicated to a U.S. Army lieutenant colonel who was also a bird watcher and artist.

Long buried under the 20th-century landscape, this lift lock of the Alexandria Canal is the lone remnant of an ambitious early American transportation project.

A massive, majestic mammal watches over pedestrians from his perch atop a former B.P.O.E. lodge.

The final resting place of an unidentified revolutionary soldier sits behind a Virginia church.

This simple stone memorial remembers a secret, Geneva Convention-defying interrogation base from WWII.

Once forgotten and built over, this historic Black cemetery now houses a poignant memorial.

Once the largest trading firm of enslaved people in the U.S., this building is now a museum that preserves Alexandria's dark past.

A former major munitions plant that has been converted into a sprawling art space.

This twice-relocated "Usonian" home is among the smallest built by master architect Frank Lloyd Wright.

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

The tomb was guarded by soldiers from both sides of the war, and some left their initials carved in the brick.

This colonial tavern played host to George Washington, Thomas Jefferson, and other famous early Americans.

This stately building in Alexandria, Virginia was built by Freemasons to honor one of their most famous members.