The most secretive body parts are muscles, which hide behind layers of skin and appear only occasionally to help to lift cars off trapped kittens. Flex your biceps in the absence of a cat emergency with today's Groupon: for $19, you get five fitness classes at Fort Washington Fitness (up to a $50 value).

Past Fort Washington Fitness's palatial lobby and burbling water fountain dwells a nationally certified cadre of personal fitness trainers, heading up group classes for all fitness levels and goals. Alive with body-buffing opportunities, the schedule offers lessons such as core-chiseling, spine-aligning Pilates mat, afterschool Jr. Fitness classes, and results-oriented Six-Pack Abs, a series of 30-minute workouts to efficiently complete beer-cooler costumes. High-energy cardio kickboxing keeps calories burning through a one-hour regimen of unchoreographed jabs, crosses, hooks, and kicks, and Fun Fitness embraces the cardio exercises of yesteryear, with dodge ball, relay races, and obstacle courses. The expansive facility affords space for private showers, saunas, and steam rooms, and free high-speed WiFi allows class members to immediately de-friend newly loose-fitting pants.