Now I understand that we have no clue as to how the planet formed currently; the most we know is what we have learned from PDA's. One immersive issue I have however, is the lack of underwater air-pocket cave systems. Have you ever done the trick with a cup where you stick a tissue inside a plastic cup, turn it upside-down, and force it under water? The same principle applies, but minus the force and just add the cave system. Now, I understand that some caves form as a result of erosion, but even then, depending on the currents and sea level, these air-pockets can very easily form at nearly any depth assuming the water pressure on the ceiling does not cause a cave in. I'm curious on other's opinions of this, and if you think it would be a nice/fun/interesting factor in the game.