This is the forum for helping you out if you're stuck in Grimrock 2 or if you want to discuss about the mysteries of the Isle of Nex. Warning: forum contains spoilers!
The latter because rope seems very handy for my alchemist who I'm using as a sort of utility/support character, and the extra Serpent Bracer is extremely helpful for the high amount of poison enemies that show up in the next area. Herder's Den was trivial for my party because I stacked so much poison resistance.
And the Thief one I chose because I was still using a stupid blow gun and desperately wanted that bow. The extra lockpicks are very nice as well; now I can open anything I want without worrying too much.
In hindsight I would say that
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Snake Charmer is a no-brainer, clearly the best choice. Everything it gives you is actually very useful. Thief I could take or leave, the lockpicks were good but you can find a shortbow nearby that's not really that much worse. Kinda regret opening it. Warrior seems utterly pointless; does anyone actually use the special moves on weapons? And the mage one seems pretty crappy except for the +10 resist all pants, those are amazing actually.
Found one gold key somewhere in the level above, presumably for that forcefield with the wand that gives +5 energy and +1 Wil. I just skipped the forcefield and used that key on the Archmage cache since the wizard upgrades were far superior. The gold key from one of the rats in the Cache itself I used on the Snakecharmer room (best room of the 4). The gold key I found in a crate at the bottom of the river in front of the castle I used for the Thief cache. It's the worst of the three, but it has two lockpicks in it as well as some arrows and a marginal bow upgrade (veterans of LoG1 will note that the bow in there was the best bow in LoG1). The lockpicks were for the secret chests above to get the Rogue hood and the bear gauntlets, which were also nice upgrades.