The New York Earth Room is an interior sculpture by the artist Walter de Maria that has been installed in a loft at 141 Wooster Street since 1977. Go see!
The best way to enjoy Manhattan is from Brooklyn. Transmitter Park offers views without the crowds, and you can pick up coffee-to-go and treats from nearby Ovenly. The India St/Greenpoint Ferry is a 5 minute walk and will take you all the way to the Rockaways in the Summertime.
AIR at Summit One is a multi-story, completely immersive environment 91 floors above the street in midtown Manhattan. A stunning, transportive world created by digital and installation artist Kenzo, it is designed to transport you to another world away from the street culture of NYC and into an alternate state of consciousness. Peak time to go is sunset, when the mirrored environment transitions from magic daylight vistas to an internal LED system that removes all sense of time and space.
Of all the many museums in New York, this one is the most striking to me because of the unique experience you have while viewing the art. This Frank Lloyd Wright building integrates art with architecture in a way that makes it unique to this city. No matter where you are standing you get an incredible, extremely thought out detail of his work and the exhibited work.