Heh, tunnelling under water is easy! :D Steps: 1 fill up on wood. 2. dive underwater. 3. build a quarters at the starting point for your tunnel. 4. dig out another 3x3 empty space. 6. build another quarters in the newly dug space. 7. repeat from step 4 until you run out of wood. 8. get more wood etc! :P The theory is simple: Quarters heal you faster than you can drown, so as long as you have cash, you're safe. Unless you're always digging through dirt, you'll always have coins from mining stone. :) There's much more you can do to improve the process, but I'll leave that up to you. ;) Hint: try playing with ladders.