Dream dimension

This is a dream. Really. This entire cave is another dimension. A dimenion you can only enter in your dreams. Many people are here at the same time, but nobody actually knows that they are actual people (since this is all a dream). You can do anything here once you're lucid - fly, jump as high as you want, let yourself fall down the cave to feel the adrenaline inside you or anything else. Once it turns day, though, the cave turns into a nightmare. Monsters appear, mimics being the most common, and will try to kill you. They mimic what they have heard and seen last. You can escape them by waking up or going to the sanctuary of people who live there. Those people are those who have failed to wake up in the morning and now have to survive forever inside the dream dimension. If you die in the dream or don't manage to wake up, you're dead irl.