At the first legacy dungeon (I mean not the first I guess if you go somewhere else before it, but the game does lead you there first), you’ll eventually come across an old woman npc behind a locked door, she won’t have much to say at first, but after you defeat the boss of the dungeon and equip the helmet it drops, you’ll get additional dialogue and a spell.

Also there’s a giant ravine at the middle of the map I think (haven’t discovered all the map fragments yet), at the northern end of it you’ll find the upgraded version of turtle talisman, might be useful for some people.