An earthwork sculpture built by Robert Smithson in the Great Salt Lake only reemerges during drought.

This rugged area of red rocks and arches is often considered one of the most beautiful places on Earth.

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

The hike through a narrow river flanked by the 2,000-foot-tall walls of Zion Canyon is one of the best in the world.

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

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

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

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

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

A daily replay of the experiment that proved the rotation of the Earth.

Erected in 1697 this Philadelphia bridge is the oldest surviving roadway bridge and perhaps the oldest stone bridge in the United States.

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.

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

Yo, Adrian!

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

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

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

Philadelphia boasts one of the best — and most often overlooked — traditional Japanese gardens in North America.

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

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

Relics of the 1894 Midwinter Exposition continue to delight visitors today.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.