France's national museum of scientific and industrial instruments.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

A haunting collection of the vanished and disappearing natural world.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

France's most famous cemetery, with some of its most curious tombs.

The last of Philadelphia's wood-paved streets is now a landmark of terrible engineering.

A tour de force of a fountain, memorializing a man who loved fountains more than anything else.

Contrary to what one might expect, ice forms inside this small cavern during the summer and melts during the winter.

This lush forest valley was once mined for lumber to the extent that it was once nicknamed "The Pennsylvania Desert."

There aren't too many operational funiculars around, but Pittsburgh has two!

Ant sculptures march up the side of what used to be an iconic spot in punk rock lore.

Yo, Adrian!

A mine fire has been burning under the deserted town since 1962, but this church is still going strong.

Over 100 concrete munitions bunkers are all that remain of a Pennsylvanian village seized by the US government.

"Dark Sky Park" is heaven on Earth for astronomers, one of the rare U.S. locations with no artificial light pollution.

A toxic ghost town sitting atop a massive coal fire.

This extraordinary Depression-era expenditure was modeled after a postcard of a Mediterranean hotel.

This Delaware River bridge is emblazoned with a catty slogan from a more prosperous time.

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

The world's third-largest crystal sphere has sat in the Penn Museum since 1927 with the exception of one outlandish theft.

Golden and naked, the figure that was once the highest point in New York is all that remains of the second Madison Square Garden.

An Irish Memorial commemorating those who perished due to potato blight.

These lush botanical gardens employ the most purrfect pest control force.

A model of a dinosaur that was named for Andrew Carnegie stands outside the museum that also bears his name.