When I start the game, this thing will just pop up for me to go into the cave. This time, it's not doing that and I know I still have about 8 - 10 hours before it collapses. I don't even have the game telling me it collapsed, but it's just suddenly gone. There isn't even an icon on the screen that allows me to get into the cave. I only had 1 (or 2?) level(s) left! How come it just vanished??