Where do I get the White Crystal key?
Based on the talk of certain characters in the pub I've figured out that I need a key to open the crystal doors. Up until now I haven't been that worried about it, assuming I'd stumble across the key eventually. However I got a quest to open one of the doors so I'm assuming the key is either somewhere on the third stratum (which I just unlocked) or in the second stratum and I missed it.
Where can I find the White Crystal key?
It's in a chest in the southwest corner of B7F, sector 1F. You have to walk over some spiky floor tiles and dodge a Moa to get to it, which might explain how you missed it.