Too poor to get into the City Club? Too female to join the Bohemian? Eighty dollars a year buys you easy access to SFMOMA's rooftop garden and cafe, one of the city's most private public spaces. On weekends, the sculpture garden is crawling with 4-year-olds, but on a weekday afternoon, the garden is the most serene square footage downtown. Through the windows, the clouds float over Alexander Calders, a lone art-school student, and perhaps a few scattered tourists, who are awed enough by the surroundings to guard the contemplative mood. With a family of Louise Bourgeois spiders as your neighbors, and your companions a Blue Bottle americano and a slice of Caitlin Williams's Thiebaud cake, an hour spent on the rooftop garden feels like one of the gifts the city sometimes springs on those of us who search out its secrets.