Cave diving is peaceful, often pioneering, but potentially deadly!  You breathe a carefully calibrated mix of compressed air and nitrogen.  World record cave dives are around 300 meters (984 feet).  It only takes 9-10 minutes to go this deep, but close to 10 hours to resurface!  Cave diving at any level is as dangerous as you make it.   At 150 meters (500 feet), the water pressure is so intense that it squeezes the nerve fibers in your brain that conduct impulses, resulting in tremors, tunnel vision, and loss of motor control.  The result is death.  Similarly, if you ascend straight to the surface from 150 meters, your blood will boil and you will die.