This unique historical monument features large concrete spheres designed to resemble fallen stars.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

An emerald-green grotto just a short trip from Austin.

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

People escaping slavery may have hidden inside a corpse vault.

Cold War intelligence agents monitored communist embassies from an attic in a former pigeon coop.

An abandoned stretch of highway, deteriorating next to the operational one.

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

Edgar Allan Poe's old dorm is now a shrine to the author's legacy.

Giant busts of 42 U.S. presidents are sitting in a field in Virginia.

Sail through this subterranean show cave that is home to a legend that would go on to name nearly everything around it.

This one-room cabin where the young colonel slept during the French and Indian War.

Despite violent work crews and massive delays this abandoned canal tunnel was built to last into the modern day.

America's first federal monument.

Home of the physician who set the leg of John Wilkes Booth after the Lincoln assassination.

Captain John Smith thought these cliffs were amazing in 1608 but sharks thought so 20 million years before him.

Rediscovered after a century, the father of the American Navy was reinterred in something dredged up from Davy Jones' Locker.

Historic home of America's sweetheart sharpshooter, Annie Oakley.

The final resting place of two (or three) presidents, one vampire, and 18,000 Confederate soldiers.

Heron, whitewater rapids, and urban industrialism all add to the beauty of this concrete nature walk.

A plaque marking the famous abolitionist's birthplace often overlooked by visitors to the nearby Charles Sumner House.

Bizarre Cavern.

The rooster who crossed the road lives on forever in Takoma Park, Maryland.

The school tested mustard gas for the U.S. Army during World War I.