It will take you just a 45-minute subway ride from midtown (plus a pleasant 10-minute walk through Fort Tryon Park) to get to The Cloisters. It is the uptown branch of the Metropolitan Museum of Art and it is very worth your trip. Perched on the tip of Manhattan, the castle-like museum is comprised of five medieval cloisters imported from France and filled with art and artifacts.
Among the works of arts on display, the most celebrated ones are The Unicorn Tapestries, a group of seven Belgian tapestries depicting the mythological hunt and capture of a unicorn. A must for medieval afficionados! Many visitors come for the building itself: one room recreates a 12th-century chapel and the monastery gardens are breathtaking. The cool, shadowy buildings are ideal for escaping steamy summer days. The views of the Hudson River are spectacular.
And hey, New York Magazine even nominated it as this year "Best Not-Cheap-Feeling All-Day-Long Cheap Date". Read more about it here. And since you are there, print this page from the magazine for more ideas to explore Wahington Heights, the neighborhood where this is located.
I am always stunned to notice that many New Yorkers have no clue this beautiful location even exists. Any best kept secret in your area?