I believe that this mosaic, as with all the others from Caracalla's Baths, is in the eastern Palaestra, which was the space where one could excercise, work up a sweat, and get one's pores opened up to assist in one's cleansing. The baths were a fascinating ritual, in many ways more interesting than, say, the chariot racing (the most popular mass pastime) and the gladiatorial games (the second most popular mass passtime) since there isn't really an equivalent in contemporary Rome (=USA). Yes, there are health clubs these days, but it's not such a central part of the ruling class' social life.