Then, I enlisted the aid of my girlfriend to help me paper mache the entire thing. Then I sealed it with PVA glue brushed on over the top!
I used toothpicks, and hot glue, to make some creepy rock formations inside the cave... I also used some screen and a few straws to make a nifty pipe and industrial area.
Lastly, I sprayed the entire board with spraypaint, after leaving it overnight to dry. I put black primer on first, then dusted it with a ruddy brown color I had left over.