Ginnie Springs is a highly popular privately owned spot for a swim and scuba diving. You can do all sorts of outdoor activities including camping and canoeing. There is an onsite dive shop that offers scuba diving training for the inexperienced.
Ginnie Springs Outdoors is located about 15-minutes west of I-75 and is easy to arrive to. If you are visiting Orlando you are within 2-hours of this amazing spot, definitely worth the drive!