This grisly headstone doesn’t seem to be resting in peace.

Look closely and you’ll notice that the color changes a third of the way up the tower.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

A building shaped like the Army Corps of Engineers logo, because why not?

Helen Keller once broke ground on this historic center for the study of technologies to benefit the hearing impaired.

100 years later, they're still down there.

A diminutive plaque recalls the treetop sniper who almost killed Abe Lincoln.

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

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

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

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

This chapel on a cliff is renowned for its healing powers and was founded on the site of a supposed divine intervention.

A once crucial portion of the Long Island railroad still lays abandoned, waiting to be turned into an urban park.

Meant to be one of the most extravagant hotels in the world, now an eerie, abandoned architectural gem in Mexico City.

Live data is transmitted from the Atlantic coast to instantly recreate the ocean waves in this fountain at the NOAA headquarters.

Enchanting cave with a river crashing through the roof.

This picturesque mansion has gone from opulent ruin to nature museum.

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

A remarkable time capsule of American manufacturing deep in Maryland coal country.

An underwater city for the dead.

St Bernard de Clairvaux Episcopal Church, better known as one of the oldest European buildings in the Western Hemisphere.

An underwater statue of Christ blesses the depths off Key Largo.

The world's only underwater laboratory where "aquanauts" study oceanic life.