It's not exactly a new playground — Helen Wills Park has been offering the denizens of Russian Hill a bit of recreational breathing space since World War I — but a couple of years ago the old girl got a dazzling facelift that amounted to a stem-to-stern, all-inclusive, cross-generational rebirth. For years the .83-acre concrete-and-asphalt playground (named after the great Bay Area tennis star and Olympic gold medalist) had been in disrepair, with a dilapidated clubhouse, little or no seating or foliage, and arsenic-based wood preservative, for God's sake, leaching into the soil. Now the concrete's been replaced with landscaped, irrigated play areas; the old bunker of a clubhouse has morphed into a cheerful all-ages rec center with kitchen facilities, ping-pong tables, and rocking horses; and there are tree-shaded benches aplenty for sitting and enjoying the fresh air. Most any day you'll find hot games of basketball and tennis unfolding on the resurfaced courts, kids of all ages clambering up, down, over, and into the ramps, poles, ladders, slides, and tunnels of the new Seusslike play structure, and chess-playing grandpas pondering their next moves.