If you have your advanced cert they will take you into some of the caves. you just really monitor your air and you pop up in sinkholes throughout the jungle. Parrots flying around above then head back down. at times you swim for maybe 10 minutes with no air pockets!! If you have experience they take you into areas where you must take your bcd and tank off and pass it through a hole and slip through, put it all on and keep going. The water is cold as this is where east mexico gets their drinking water from and its as clear as you can get. no particles or life in the water just the most amaazing calcium formations . cant explain til you do it. MORE PICS
http://www.hiddenworlds.com.mx/caverngallery.html