At its best, a swimming pool is a rectangular waterhole, an aquamarine gathering place where the social rituals are played out with all of the underlying rigor of village life in Kenya or Bolivia. There's something about a gently rolling body of water that promotes communal ties. Nowhere is this more evident than the 75-foot pool at the heart of Jefferson at Young Circle, a 235-unit apartment complex in downtown Hollywood. The morning begins with preschoolers taking tentative steps into the shallow end as nannies or stay-at-home moms compare kiddie notes. By midmorning, the first of the sunbathers are out. They stretch out on chaise longues and dig into magazines and bestsellers, with the Walkman plugs coming off as friends stop by. On weekend afternoons, the picnics and birthday parties get started under the shade trees near the back, and a few rowdy kids play loud games in the water. Lots of Spanish, lots of Portuguese, plenty of beer. In the late afternoon, a service supervisor from a local car dealership strolls out, cell phone glued to his ear, and eases into the Jacuzzi. On hot nights, the parties extend well past sunset. At 2 a.m., two young men from Long Island, stockbrokers in training, do cannonballs into the water, which is luminous with submarine light, to punctuate an evening of barhopping on Hollywood Boulevard. A couple of lovers ease their way, hand in hand, into the spa. Then all is quiet, and the pool lies still, its blue surface quilted with soft ripples. Of course, not everyone can enjoy this sublime calm. Want to get in? Rent an apartment in the complex, or get invited by someone who's a tenant.