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

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

An eerily abandoned stone tower is all that remains of a demolished dam on Cape Fear River.

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

A derelict bit of transportation infrastructure hidden in the woods.

The national park was once a plantation estate.

The Pentagon sits on a former island that was in Virginia at low tide and D.C. at high tide.

A double agent hid information for the Soviet Union beneath this bridge for more than 20 years.

The remains of a historic plantation nestled in between a parking lot and the rental car return at Reagan National Airport.

Exact replica of the ancient monument, but much, much lighter.

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

This pre-Revolutionary War grist mill ground corn and flour for soldiers in seven American wars.

This Virginia railway overpass is said to be haunted by a serial killer in a rabbit costume.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

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

A railroad tunnel that, upon its completion, was considered one of the engineering marvels of the modern world.

Rotting dome home spotted near Chapel Hill, North Carolina.

A retired tobacco farmer's pet project turned into a sturdy miniature city.

Hidden for 165 years inside a building designed by Thomas Jefferson are the remains of what may be America's first educational chemistry lab.

The ruins of this Thomas-Jefferson-designed mansion have been left to crumble since the Christmas Day they burnt down.

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

This woodland architectural installation acts as a camera obscura for the heavens.

The only known Futuro house in North Carolina sits along a stretch of desolate highway on the Outer Banks.  .

The remains of a failed attempt at medieval nerdery are hidden deep in the woods of Virginia.