One of the best kept sightseeing secrets in NYC, the Cloisters part of the Metropolitan Museum (see url: http://www.metmuseum.org/Works_Of_Art/department.asp?dep=7). This is a French medieval castle overlooks the Hudson river. Located in upper Manhattan in Fort Tryon Park this magnificent castle was built by John D. Rockefeller. This building was brought over piece by piece from France to house his vast medieval art collection he then donated it to the Met in 1925. This place is usually very quite and peaceful, and rarely crowded.
You owe it to yourself to see this. If you have a car its no problem getting there and there is plenty of parking (which is free!). Getting there by subway is not EZ, better to take a taxi. Most cabbies don't even know of it. Tell your cabbie to go north on the Westside Highway to the Henery Hudson Parkway. Then just befor you leave Manhattan for the Bronx you'll see a sign for Ft. Tryon Park, take that exit.
Best time to go is in the spring as there are courtyards overlooking the Hudson and the George Washington Bridge. This museum is located in the Washington Heights part of Manhattan which enjoys the highest evaluations in the City. The views from the open French-Italian courtyards are wonderful and there is coffee and pasties avalibel for a light lunch.
Great for parents that want to expose their children to a European world this side of the pond or couples looking for a romantic afternoon.