A few years ago, Amy Dantzler, an accomplished open-water swimmer, and her wife, Julie Anderson, got in the habit of taking early-morning trips from their home in the Hollywood Hills to L.A.’s South Bay. “Amy would get up at 4:00 a.m. and drive to Manhattan Beach because all the pools were closed,” Julie says, reflecting on the early days of the Covid pandemic. “Sometimes I’d join her to run on the sand. One morning I turned to her and said, ‘Why don’t we buy a house down here?” Amy, a real estate agent, liked the idea a lot—so much that she floated it by Bryan Libit, an architect and interior designer from go_sml who frequently joins her for a swim. “We were walking back to the car from the beach one day and saw a For Sale sign from the street,” he remembers. The property had stood there since 1964, its clean-lined, A-frame structure the epitome of midcentury cool. But sometime in the intervening decades, it had been turned into an unpermitted rental duplex. Nevertheless, Amy knew tha...