Twilight Caverns is a 4 level deep cavern located north of Kaymo Mountain. If you go inside it while being below level 40 all the monsters will attack you as soon as you pass them. If you want to visit the second level or higher you have to first reach level 55 with your character. As long as you haven't reached that level the game will let a tiny window pop up where it says; Requires level 55.