Oasi della Pace
A rather bucolic choice of swimming pool set among hedges and cypress trees.
For Olympic-sized open-air public pools head to the suburbs, either in EUR or off the Appian Way. If you stick to the centre be prepared to pay for the privilege, especially if you go to a hotel pool to swim. If you just want to laze and lounge over a few cocktails head up to the Radisson SAS rooftop, which is free.