The striking Solomon R. Guggenheim Museum is an artwork itself, its bulbous facade an unmissable feature of 5th Avenue thanks to architect Frank Lloyd Wright. Inside, there are 17,000 artworks to admire and, luckily for weekend visitors, entry to the museum is free on Saturdays between 5pm and 8pm—just enough time to enjoy a few Cezanne, Kandinsky and Gauguin masterpieces.