This remarkably intact, 260-year-old cargo ship is only visible at the lowest of spring tides.

Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

This architectural stunner is one of the few surviving Egyptian Revival theaters in the U.S.

This whimsical home made entirely from clay is basically a giant piece of pottery.

The unusual lighthouse looms over waves of prairies with no sea in sight.

The randomness of this wall of lava lamps helps encrypt up to 10 percent of the internet.

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

Volunteer-run library dedicated to exploring five decades of activism history.

This rusting remnant of the local herring industry is being given a second life.

This lab's maddening silence is good for business but bad for sanity.

A cluster of granite granaries perched on stilts.

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

Military and first responders can test their skills in a Foggy Bottom mock station down in Georgia.

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

A Beaux-Arts triumph rises from decades of decay to become the heart of a new innovation district

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

A stunning, abandoned limestone quarry in southern Indiana provided the stone to erect the Empire State Building.

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

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

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

Geodesic dome luxury retreat in the Scottish Highlands.

19th-century operating theatre in which the use of ether was first demonstrated - plus, a skeleton and a mummy!

Designed by Buckminster Fuller, this relic of the 67 Expo survived fire and ice.