Great game! Uhm...on which level is the Helm?

[Atticus]

I've made it clear down to the Bone level and I've completed all quests except for the initial one, the Helm of something/whatever. I'm supposed to bring it back to the merchant guy and give it to him so he can take it to the king.

I've cleared out all the levels, but can someone please tell me which level I need to go to to find the Helm? I'm a bit unwilling to go back through every level, opening every crate in every room that I might not have had a key for.

Thanks for saving me a few hours!