You can’t quite wear your birthday suit to Banya 5. In deference to the spa’s co-ed policy, swimsuits are required. But the compact network of well-kempt saunas, steam rooms, and hot tubs delivers everything else you might want for a very serene celebration. And if devotees of the Slavic sauna tradition are right, broiling in a hot room before plunging into a frigid pool might just keep you feeling like there are fewer candles on your cake. HANNA RASKIN 217 Ninth Ave. N., 262-1234, banya5.com