Swan Gymnastic Center
Via dei Pepi 28, Florence
Located in the center of Florence (within a short walk from the Dome), this practical gym welcomes all tourists with a day pass. For 12 euro a day, you can workout using cardio equipment, free weights or take any of their classes.
From Pilates to body sculpt, circuit training and fit box, the morning and evening sessions will keep you busy.
The training area is quite small and usually crowded: some cardio equipment and a bit of room for free weights, but I highly recommend their classes: they have good trainers and the body sculpt and GAG sessions are meant to tone you up pretty nicely, if you use the appropriate weight for dumbbells and barbell.
Find them here: http://www.palestraswan.net/