I don't dive, at least in the water, and closed in spaces get to me but thought I would share this. We have what are called 'sinks' here in FL which are basically sinkholes where the ground has collapsed. Some are water filled by springs. One well known one is Wakulla Springs. These guys were part of a team that checked out and followed 6.9 miles of underwater caves until two sinks were seen to be connected ( as I understand it Jablonski is one of the divers in the good Dr's book)Not sure if anyone had watches on but the trip seemed unbelievable.