This virtually windowless mass of smooth concrete is the only Catholic church in the city.

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

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

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

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

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

Yo, Adrian!

The walls of the iconic dome are hollow and have a secret stairway.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

The "lovely red Vega" of the legendary record-settling pilot.

The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.

This shale formation along the Appalachian Trail once inspired the third president of the United States.

This advertisement for talcum powder was painted on the rock face and has since defied removal.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

Despite violent work crews and massive delays this abandoned canal tunnel was built to last into the modern day.

On top of a resort town as old as the Bronze Age sits an incredible war memorial statue overlooking the beaches below.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

Started as a kitchen garden, now the second largest botanical garden in the world.

This futuristic German spa allows visitors to float in a pool of salt water while zoning out to underwater techno.

Behind an abandoned storefront is an example of pioneering 1930s gas station architecture.

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

Light bulbs, scrap wood, and tinfoil comprise this homemade throne of the gods.

Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.

Largest Roman Catholic church in North America.