National Academy Museum and School
Combine a museum, an art school, and an association of artists and architects all in a Fifth Avenue mansion and you get the National Academy Museum and School. View a collection of over 7,000 works of 19th, 20th, and 21st century American art for free through the Museum Mile Fair - usually a fee is required for admission.
National Academy Museum, 90th Street and Fifth Avenue
[Photo via @nationalacademymuseum]