This once-grand marvel of engineering is now 41 miles of scenic hiking trail.

Decades after testing the polio vaccine on unwitting patients, this historic mental hospital sits in ruin.

The abandoned husk of a mental institution that failed to save a Jazz Age icon still sits nearly unchanged.

The library of every book lover's dreams.

This mouldering abandoned mental hospital was once a center for progressive healing.

These World War I shooting range tunnels are now haunted halls of underground graffiti accessed through the roots of a tree.

This abandoned factory on the Hudson River once churned out a million bricks a week.

Surprisingly aquamarine waters fill deep lakes formed at the end of the last ice age.

This Manhattan museum houses one of the largest collections of Spanish art and manuscripts outside of Spain.

Hundreds of numbered stakes hidden in the woods mark the graves of the lost souls of a nearby asylum.

This once-private estate is now a dreamy, meditative garden that's open to the public.

Spiral-bound community recipes and antiquarian gems mingle at this small East Village shop.

A young woman's senseless murder led to the controversial psychological theory of the "bystander effect."

A 16th-century Andalusian palace.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

Three bridges and one giant canyon make up this fantastic Spanish settlement.

This semi-secret storybook hedge maze is also the oldest garden in the city.

One of Antoni Gaudí's least-visited works, an homage to Catalan patrimony that mixes neo-Gothic with Modernista forms.

Occupied for six centuries by Franciscan Order nuns, this monastery is an amazing ode to Catalán Gothic architecture.

A stately palace has been converted into the world's largest cannabis museum.

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

A legendary speakeasy bookstore returns from the brink.

A miniature rainforest is growing inside of a Midtown Manhattan office building.

New York's oldest magic store.