In Sipadan there is a cave right off the end of the dock at the central resort. As Elbert said, BIG sign that said DO NOT ENTER. And we didn't!
In Palau they told us they were going to take us to Chandelier Caverns. Now who would think cave? We entered at 20' - surfaced, looked around, went down through another opening, did the same thing and proceeded on into the third and final cavern. The walls were quartz and limestone with stalactites sticking down. Our lights lit the place up like a ball room. Water dripped off the tips of these and was actually hot - and fresh. There was a layer of fresh water a foot or so thick floating on the top of the salt water. The pictures people took make it look like we were suspended in space.
There was the diver master and eight of us when we started. As we bobbed around in a circle on the surface of the water I counted - eight! I called out to the dive master "Who's missing?" Nobody seemed to care. This upset me.
The dive master was stoned on Beetle Nut and my dive buddy, Patti, next to me was freaking out. When she screamed that she had to get out of there we started donning our masks and mine was missing. One of the guys saw it being swept into a small opening and grabbed it just in time.
When we entered the third cavern on the way out I was suddenly in total blackness. It was more than darkness, it was blackness. I had a light in each hand and just turned in circles trying to see anything.
There was a hand on my elbow that lifted me up just inches into crystal clear water looking at the opening to the surface. I had followed the dive master both in and out and at this point I had let my fins touch the bottom and the silt was all enveloping.
Patti will never go into another tunnel, cavern or what ever you want to call them. I will, but I sure do know what they mean by silt! Now I know to just pop a little air in my BC (or take a deep breath and hold it) to go up a little. BTW - our missing eighth person said there was so much silt kicked up that he had backed out at the beginning.
I had a dive master take me through a series of caverns here in Belize that became too small for this fat lady and I had to back out.
I have a friend who entered what looked like a cavern in the Channel Islands in California and was swept all the way through to the other side of the island - out to sea. He's lucky another boat found him. He will not get near any opening in the reef.
The important thing I think is for each and every one of us to know our limitations and I think it is very important that the dive masters are clear in their dive briefings.
Sorry - I do get carried away.