The first piece of public art dedicated to LGBT rights.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

An abandoned 19th century quarry in the middle of the woods, remade by unnamed wanderers into a massive series of rock thrones.

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

Yo, Adrian!

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

Huge masonic hall in Philadelphia with lavishly themed rooms.

The sounds of the world's largest fully functioning pipe organ dazzle shoppers at a Philadelphia Macy's.

The first American department store, and home to the largest operating musical instrument in the world.

This elaborate towering structure was once famed for its revolutionary height.

A clone-tree in Washington Square Park sprung from seeds that went to the Moon and back.

Mural made of 100,000 pieces of hand blown glass, and one of the largest glass murals in the US.

This charming colonial alleyway is one of the oldest continuously used residential streets in the U.S.

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

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

This little-known collection holds everything from "Dracula" notes, to the manuscript of "Ulysses," to the forged works of Shakespeare.

The floor-to-ceiling collection in an old factory is a unique alternative to stuffy galleries.

Twenty-three trees, each paired with a basalt stone, line a street in Chelsea, continuing an urban project started by German Fluxus artist Joseph Beuys.

Contrary to popular belief, this secluded statue doesn't represent Pennsylvania's founder.

This translucent sculpture represents a quintessential component of New York City's skyline.

New York City's only wildlife rehabilitation center treats more than 3,000 feathered and furry patients each year.

There's a piece of New York City transportation history hidden in plain sight at a Manhattan subway stop.

This nearly invisible wire transforms much of the city into one big, symbolic home on the holy day.

Perhaps the most scandalous statue of America's first president.