Descending into this sublevel hideaway is like stepping back in time to a particularly festive Havana nightspot circa 1947, complete with thrumming congas, frosty Mojitos, a brick-lined courtyard, and the fragrance of smoldering cigarros perfuming the night air. There are perhaps a half-dozen public establishments within the city limits where you can puff on a stogie with equanimity, and the snazziest has to be 850. The tiled, rough-beamed, shell-pink setting is dominated by a handsome old bar at which a variety of tapas and Caribbean concoctions is skillfully dispensed, and a small area where irresistibly danceable mambo is offered up every Friday and Saturday night. The large fountain courtyard is an excellent place to pass a warm spring evening, and two adjacent billiard rooms and the perpetually stylish clientele offer further distractions. There's a nice selection of cigars in the humidor up front, and since the open layout of the place keeps the smoke at a minimum, even the nonsmokers will enjoy reclining in a wicker armchair, sipping a daiquiri, and listening to the congueros.