One of the oldest used bookstores in the U.S. has been selling antiquarian treasures since 1825.

A morbid secret lies hidden within the beautiful walls of the Boston Athenaeum.

One of the oldest of its kind.

The body of St. John Neumann and his collection of hundreds of relics, on display in a Philly church.

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

South Philadelphia is home to Keith Haring's only surviving in situ collaborative public mural.

One artist's love letter to his city and its citizens plays out across dozens of bright murals painted on the sides of decrepit buildings.

Final resting place of the immigrant who brought artificial seltzer water to America.

A mysterious, abandoned building rotting on the Brooklyn waterfront.

An abandoned subway tunnel that could have reinvigorated Staten Island still lies somewhere beneath this Brooklyn park.

The name of this famed hospital was once a byword for the horrors of medical and psychiatric care.

A celebration of capitalism in Midtown.

The oldest operating apothecary in the US has treated everyone from Thomas Edison to Mark Twain.

After immigrating to Paris in the 1970s, two brothers from Laos built a grocery store empire.

This life-size replica of the Statue of Liberty's flame is also a tribute to Princess Diana by default.

The first green space constructed on an elevated viaduct.

Statue of death tucked in the University of Medicine courtyard.

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.

The history of radiation is on safe display at the foot of a radiation science laboratory.

France's national museum of scientific and industrial instruments.

A haunting collection of the vanished and disappearing natural world.

The world's largest wooden structure.

The first tunnel to be dug beneath a river, repurposed as an art and museum space.

There's an exclusive Beefeaters pub hidden in the Tower of London.