On my 4th OW dive a few months ago, I had a bad experience with my buddy and I getting lost, accidentally going into a cave, and almost running out of air (on the same dive). So the story goes, we were supposed to navigate through a narrow channel that went parallel with the beach, turn around, and come back through the channel. Well, going through it was fine, it was when we were coming back we had the problems. The vis was pretty poor, my buddy and I had to hold hands not to get seperated. But one thing we didnt notice on the way through the channel/canyon, is that on the way back there was going to be slit like smaller canyons on the side of the main channel. We couldnt tell they were the wrong places to go, because the vis was only a few feet. We kept going in them until we noticed they kept stopping, then we would turn around and try to find the main canyon. There were a lot of divers from our class and "TA's" (teachers assistants) so we kept running in to them when we would find the main channel. When I noticed a TA swimming by, I grabbed him and let him know we were lost and were on the low end of air. He must have thought we hadent gone to the end of the channel yet, so he led us through it one more time. I then pointed to my air and tried to explain that we needed help getting back (this has all happened in about 20 minutes). He pointed us in the right direction and we tried to get back on the right barring of our compass. We finally found where we were supposed to surface and surfaced with only 200psi for my buddy, and 650psi for me. I dont think I will ever go into that canyon/channel again, or at least not for a while.