I just battled all the way through Ilona's dungeon and killed the sea creature looking guy, Cyrion or something. However there's a chest down there I can't open, does anyone remember where the key is?

I found a composite key on an earlier level of the dungeon but I never used it, does anyone know what this is for?

"I've never been a lover, I've always been a fighter. It's high time I fight for love instead of the usual crap reasons I fight for, like my own pride" -- A wise guy