The Clark Museum in Williamston Massachusetts (also known as the Clark Institute) is probably the most beautiful art museum I have visited so far. The outside grounds alone is already picture perfect and serene.
Inside the 11,000 sq. ft of gallery space is filled with huge (as in huge) collection of European and American paintings, sculpture, prints, drawings, photographs and decorative items from the 14th to the early 20th century.
A day is not enough to savor the whole museum.