A serene park and museum in Manhattan
The Met Cloisters is an art museum owned by the Met that boasts religious (mostly Catholic) art from a range of time periods as the building used to function as a cloister for monks. The inside of the Cloisters museum is a castle-like building that can be visited for a small ticket fee (suggested donation).
There is an ample amount of green space that surrounds the museum that is open to the public and accessible by public transit - the A train has a stop in the south part of the park and there are busses that drop off and pickup passengers right at the entrance to the museum.
The Cloisters overlook the Hudson river on the west side and Washington Heights on the east, don't miss this landmark when in New York.