I don't know much about freediving from a technical side and I know even less about SCUBA. I taught myself to freedive at Blue Springs in Orange City, FL and have been diving there for years, never going past 60ft. I found some info on the web about a place called Blue Grotto Springs and am thinking of going there. They advertise something called an "air bell" at 30ft depth, sounds to be intended for SCUBA divers, but none of these springs ever mention freedivers anyways - only SCUBA and snorkel as far as they're concerned. What exactly is the air bell? Has anyone been to BG or a place with a similar bell? Is it what is sounds like, some huge inverted dome full of air? Would it be safe to freedive down into it and come up for air? Obviously if you did breathe that air, you'd have to re-ascend slowly and exhale the whole way... even I with my limited technical knowledge know about decompression syndrome or whatever it's called - I'm pretty sure it's *possible* to ascend 30ft with with pressurized air in (leaving) your lungs, if you do it right, but I'm not sure if it's something that's wise to go out and do 20 times in a day for recreation.