Again with the timed mine bashing!! It's not really that bad, just use your first go to map it a bit, scope out the dead ends that are as far as I remember all chest rooms, then use the map to get the quickest route thru. Remember you don't gotta kill everything in there, run past a few fights!
The Chest Key can be got shortly, when you get thru the timed mine, SAVE, there's about the toughest boss so far in the next room! I'm not gonna spoil it for you but when you beat that boss you get the Tearose Sigil, that gets you access to further down into the Iron Maiden B1. Go there, get by a couple of bosses (naturally!) and you'll get that key. It's worth the extra fighting, tho not essential, the Chest Key chests have some decent kit!
By the way, when you use Analyse, you get ALL the enemies stats, not just those immediately seen in Status, press square to see their affinity and type weaknesses, ideal for choosing weapon types!
Story keeps getting better Nick, tho I'm not sure whether voice-overs would have suited it.Very few games have good voiceovers, you just know Ashley Riot would end up talking like some punk kid like Ash from Pokemon! Noooooo!!! :0
Anyway, lemme know if you need any help, I can give you spoiler-free hints, you might see some on a walkthru.