After a three-year hiatus, SFMOMA has unveiled a Snøhetta-led expansion that makes it the largest modern art space in the nation, easily housing entire floors of abstract American art and minimalist and pop art. There’s an entire gallery devoted to Alexander Calder, with a focus on his work between the 1920s and 1960s. The Pritzker Center for Photography dedicates about 15,000 square feet to photography, more than any other U.S. art museum. The open-ceiling seventh floor houses nothing but contemporary art. Nearly 45,000 square feet of the museum's ground floor galleries are free and open to the public, and admission is free for visitors 18 and under.