you first need the amulet from the witch or lizard priestess/othra in which you need 5 glowshrooms from the entrance to the northcrest cave, which once you have them just go talk to the witch or othra and they'll have the option to talk about sunlight source. Then you get the new amulet and wear it while going into the caves and eventually you should find a area where you have the option to explore a new area in which it enters a place where you choose to go up down left or right. You explore there.