The walkthrough for chapter 12 is split into two parts because it was too long to fit in a single post:
Part I:
viewtopic.php?f=139&t=6485Part II:
viewtopic.php?f=139&t=6484Regarding the chest, I assume you’re talking about Chapter #12 Part II, #71? Where going to sleep causes it to snow, and any unopened chests get covered by a fresh layer of snow?
There is a locked red chest in the large area before with a Tyrant Mask, which requires the Ivory Key to open. Step #71 details the key location, and step #70 details the locked chest location. I think it was in a large, fairly open area, in the like bottom left-ish part, but I couldn’t say for sure.
There is also another chest somewhere close to the sleeping area that is an Easter egg I believe. I think on a rooftop area?) Indinera sometimes puts chests on the map with no way to actually reach them or open them. LF1 chapter #1 had like 3 or 4 chests like that; they’re all just teasers as far as I know.
If you're referring to another chest than one of the two above; I would need more details about it. Location, color, etc., to provide a better answer.
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Lady JJ: For LF3, I could not get a hold of Litlebro for permission to edit/repost their walkthrough, so my post for LF3 is just the update notes, which have to be used alongside the walkthrough. (Rather than a wholly updated walkthrough like LF1 and LF2 got, unfortunately)