Bay seniors know that Ocean Beach is not much good for sunbathing. The sand, however, is excellent for the construction of castles and other whimsies. This Saturday, Leap, which provides arts education programs in local schools, hosts its annual Sand Castle Contest out here below the Cliff House. Teams of engineers, architects, designers and elementary school kids will be competing to amaze you with their creativity. This year’s theme is Things That Jump. 10am to 4pm. Free.