An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

One of the U.S. Forest Service's only mansions is outfitted with a dinner table for floating food.

This stone tower marks a lookout point over the historic Washington Crossing, and maybe some buried treasure.

This Pennsylvania cave holds evidence of the oldest known inhabitants of North America.

It would take 35 firetrucks to fill this enormous glacial pothole.

This little-known Revolutionary War fort is supposedly haunted by the ghosts of its past.

The internal railway of one of the biggest steel plants in America has been transformed into a linear park with unique industrial views.

The origin of this mechanical boy was a mystery until he revealed his maker by writing it in perfect cursive.

Century-old shop, specializing in Occult products.

In the bowels of a 19th-century brewery lurks a fine-dining restaurant offering an array of themed feasts.

Mural made of 100,000 pieces of hand blown glass, and until recently, the largest glass mural in the US.

South Philadelphia is home to Keith Haring's only surviving in situ collaborative public mural.

A wall of chewing gum moonlights as collective art.

A museum dedicated to the history and exploration of both popular music and science fiction.

The magic's in the hole!

This giant iron playfully pays tribute to an early 20th-century architectural trend.

A wonderful display of arts and crafts handmade by local artisans in the Southern Appalachians.

The U.S. Supreme Court's secret Cold War relocation facility in the mountains of North Carolina.

This remarkably well-preserved Egyptian plinth is pretty well traveled for a giant piece of stone.

A marvel of Byzantine engineering under the streets of Istanbul.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

The yawning maw of this pagan visage is said to bite off the hands of liars.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The Pennsylvania shopping center was once the setting for the 1978 film, "Dawn of the Dead."