This unique building in the main square stands out among the city's typically Baroque architecture.

The king of U.S. high points towers over every other peak on the continent.

The first declared National Monument in the United States.

The granddaddy of all tourist traps, built on ice water, jackalopes, and a giant dinosaur.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

A town honors its legacy of traditional American Indian pipe carving with one gigantic pipe.

Current docking place of the SS United States, the fastest transatlantic ocean liner.

A layered tribute to the work of mosaicist Isaiah Zagar.

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 until recently, the largest glass mural in the US.

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

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

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

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

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

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

Dr Barnes' $25 billion private collection of art and arboretum.

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

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

Step inside Lucy, the world's largest "elephant."

Kentucky's anomalous peninsula projecting into the Mississippi River, site of legendary earthquakes and local feuds.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

This single room has survived the centuries with almost no deterioration.