A swimming hole in the historic industrial quarry that supplied the marble for the Baltimore Washington Monument.

This quarry filled with 65 million-year-old limestone is now home to a nature reserve.

This abandoned limestone quarry now provides visitors with multiple, breathtaking viewpoints.

The timeworn "Yankee Stadium" of the fastest game in the world isn't going anywhere.

Former villa and estate of James Deering developed to preserve native tropical forests.

This beautiful Miami garden was designed as a laboratory for tropical plants.

The only swimming pool listed on the National Register of Historic Places is emptied and refilled each day with naturally filtered water.

An enchanting natural wonder in Puerto Rico's Camuy River Park.

Hideout of thieves, monks, and goat-footed gods.

World's largest cave was only discovered in 1991, and now offers tours to the public.

Burial grounds for more than 1,000 bodies deep under the modern town of Rabat.

This otherworldly church spire reaches up toward the heavens.

The ruins of a 19th century shelter run by the Independent Order of Odd Fellows.

A remarkably opulent mansion with a tragic history.

An abandoned concrete jungle surrounded by a lush park.

The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

A blunder resulted in these charming stone-lined streams becoming the target of a Nazi bombing.

Although now a decaying ruin, this stone cabin's history includes several notable figures.

This unassuming tree stump reportedly traces its roots to the famous pharaoh queen's reign.

Charlie Smith was almost certainly not 137 years old when he died, but why let that get in the way of a great story?

The remains of an abandoned dinosaur theme park litter the woods just off the highway.

The rusting remains of the largest assembled WWII fleet on the West Coast.

An abandoned stretch of elevated road in the middle of the Brazilian jungle.

The gutted remains of this Estonian mansion are a monument to a tragic love.