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

A layered tribute to the work of mosaicist Isaiah Zagar.

World's first "penitentiary," meant to be humane, drove men insane.

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

The oldest surviving botanic garden in the United States.

This network of conjoined cellars was riddled with traps and supposedly allowed the townspeople to pretend their homes were deserted.

There was a top secret plan during World War II to seal a group of soldiers inside the rock.