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.

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

The site of the climactic scene from the classic horror film is now a historic landmark.

The United States Capitol's former columns still stand.

An overgrown garden stands as a grim marker of an unrealized dream.

A former mental hospital founded in the 1930s by a eugenicist who advocated for the forced sterilization of patients.

Recorded as the first person buried in Arlington Cemetery.

One of the Treasury Building's original columns now sits as a garden monument in the middle of a busy military base.

A glimpse into the sacrifices of military members during World War II.

A weathered, American Foursquare-style house originally built for lumber merchant William Wimsatt.

Get up close and personal at this Fresnel Lens.

A lightship turned museum, outfitted with artifacts from the vessel's past as part of the U.S. Lighthouse Service.

This field of concrete was once an active defense site armed with nuclear warheads.

The solitary grave of a schooner captain killed by lightning while serving biscuits.

Metal dinosaurs lurk in a sculpture garden on the outskirts of a popular resort town.

This homestead was occupied by Union soldiers, who believed the owners were signaling Confederate forces.

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.

Memorial stone for GWAR vocalist, depicted in his iconic costume.

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

The last of nine massive kilns that produced many of the red bricks for buildings in Washington, D.C. and northern Virginia in the early 20th century.

Anna Anderson spent most of her life claiming to be the lost Romanov child Anastasia.

A memorial dedicated to a highly decorated Marine and Korean War veteran, who also happened to be a horse.

This little brick tunnel built by Confederate forces was used to conduct surprise attacks on the railroad.