Europe’s most powerful hot spring supplies the surrounding region with hot water.

What appears to be an ordinary bridge is actually a rare aqueduct.

An abandoned Jewish sanatorium is tucked within the woods of Poland.

The world's first jet-powered aircraft were assembled by the Germans in this secret factory in the forest during WWII.

Hidden in the forest are the crumbling, graffiti-covered remains of the factory where most of Germany's explosives were produced during World War II.

Originally slated to become a luxurious resort, this structure is now a graffiti haunt reclaimed by nature.

Ancient serpentine sacrifice holder that has stood the test of time.

Legend says this sculpture commemorates a brave baker who rescued the city in the Thirty Years' War.

Deep in the forest next to Augsburg are abandoned bunkers and bullet traps from the region's military past.

Curious crustaceans support an obelisk from ancient Egypt that now stands in modern-day Central Park.

The site of the deadly Triangle Shirtwaist Factory Fire.

The most confusing clock in New York.

The feral felines of Roosevelt Island have a small army of allies and an abandoned hospital all to themselves.

The name of this tiny pocket park tucked between two buildings on Manhattan's Upper West Side is Latin for its location: "seventy-one."

A three-story copper skybridge connects two Manhattan buildings with Art Deco luxury.

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

Twice a day one of these tragic bronze mariners drowns with the tide to remember all those the sea has taken.

This anonymous businessman sculpted in bronze became an enduring memorial after 9/11, and had been mistaken by rescue workers for a survivor in the rubble.

A clock set into the concrete outside a Manhattan jeweler has been telling time underfoot for over a century.

Walk into the 19th century without leaving Brooklyn.

Where the Monitor was launched and ushered in the age of the "ironclads."

Once a ferry dock, radio transmitter, and now a new Greenpoint park.

Feral cats keeping the rodent population at bay all across Greenpoint waterfront.

A drawbridge named for a potentially intersex Polish national who fought alongside George Washington during the American Revolution, and an example of "Pulaski Red".