I managed to make it to the fourth level of the dungeon. Right before the end of the third floor, I was extremely low on antivenom, all my characters were low on hp, and I'd basically spent the last hour fighting spiders. Now, enemies don't respawn in this game, so I figure I'm safe and go to rest in a corner after sealing all the doors that lead further into the level. I get woken up with critical damage from a spider, they're fucking everywhere. Apparently at some point, maybe based on the time I'd been in the level, a secret door had slid open earlier in the complex and while my characters were taking a nap spiders had skittered through the maze and hunted me down. I killed the last spider with only my mage left, and only with a sliver of HP. After going back to res my party at the healing crystal, I do a once-over of all the rooms I'd been in and a 4x4 secret room had opened up. There's just an herb in this room but I figure there's gotta be more so I start looking over the walls. I find a switch, which opens up a hidden passage that leads to a secluded area on the next floor. At the end of the hallway is a gargoyle with an open mouth and text on the wall that says 'FEED ME'. There's two adjacent doors, one I can open with a pullchain and one that's sealed. So I go into the pullchain room and it's a maze made up of iron grates, filled with green slimes. They can attack through the grates, but I can't hit them, so I have to carefully plan my movements so I'm not getting pounded by slimes and lure them out one at a time because they hit really, really hard. I finally clear the room, find a huge green gem which I take back to the gargoyle and put in his mouth. Bam, secret treasure room, hidden behind on a secret floor behind a secret wall, hidden in a secret room that opened on a time delay.