One of Philadelphia's largest murals resides hidden under this bridge.

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

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

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

Alexander Hamilton’s creation caused quite a bit of controversy.

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

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

An 18th-century Spanish watchtower made entirely of seashell and concrete.

Once the site of the Hawaiian monarchy, this building was originally designed as a palace.

A tunnel of hardened lava along Maui’s famous Road to Hana.

The front yard of an Upper East Side town house hides the last fragment of one of New York's most famous theatres.

This miniature village stays behind in the Breuer Building, even as the museums around it come and go.

The oldest bibliophilia club in America, with exhibitions on historic books and graphic arts.

Though the case is scorched and the buttons half-melted, this hardy handheld gaming device can still run a game of Tetris.

A small peaceful park and waterfall tucked amid the urban grind of Midtown Manhattan.

More than 300,000 historical artifacts from the famous music venue, from Duke Ellington's handwritten score to The Beatles' booking slip.

Slyly buy a shake in the Parker Meridien lobby.

A simple midtown bar was once the home of a secretive and exclusive club staffed by "bunnies" under Hefner's strict rules.

Long the exclusive domain of birds and vagabonds, this little-known Central Park peninsula is open to the public once more.

Two large-scale sculptures of Adam and Eve greet visitors in the nude at the Time Warner Center in NYC.

Tucked away amidst some of the most famous addresses in the world is New York’s only fraction of a street.

Once one of the world's great cities, Cahokia was a place of religious worship, trade and mass human sacrifice before being mysteriously abandoned.

Fresh wooden posts have been added to ancient holes to recreate a primitive henge clock.