NEW YORK CITY is home to so many spas your head'll spin just trying to make a decision on the fly on which one to visit. They run from high end to low brow, medical, pleasure (no, we don't mean happy ending...), detoxifying, indulgent... all of them exist within the space of one little island. Recently we visited a newish hybrid green-medical Spa Merge on 57th. It's attached to hotel West 57 in an unassuming store front sandwiched between a Duane Reade and the lobby. The spa manager and most of her staff are from a well-known local spa on the Upper East Side and thus the spa has garnered a slew of loyals who have followed them to this corner just a block south of Central Park and we can see why.