Spectacular spa is one of the few places where you are expected to devote every day completely to yourself and not feel guilty. The people who work at spas constantly pamper you, provide you with luxuries, and gently coach you to follow a healthier lifestyle. The word "spa" used to denote a health resort with access to a mineral spring. Not anymore. Today's spas offer a variety of styles: the traditional fitness spa, the 80 IN STYLE No longer just for the rich and jaded, nowadays a spa-vacation is for everyone. Herewith, a guide to the country's 12 most popular spas and what each offers. BY RUTHAN BRODSKY pampering-and-beauty spa the international-style spa, focusing on therapies and water treatments, the resort spas, the spa-centers for behavior modification and spa-at-sea cruises. Although spas vary, they all focus on fitness and take us away from our daily stresses. Pack light is the rule for most spas. Unless you're staying at one of the few formal spas or in a resort area, dress is generally informal and relaxed. Required clothes are lots of socks, leotards, tights, a couple of lounging outfits and swimsuits. Leave the jewelry at home.