So, I decided to go for the second lieutenant, whose lair happens to be located in grasslands (or grasslands with groves, I don't want to leave it to check). Anyway, there are these "rural storage buildings", and every room inside contains like 1-4 Small Chests and each of those contains a random enchant (including good stuff with a green bar). After exploring two such buildings I upgraded every slot, basically, some slots several times. It feels pretty broken.
By the way, I even accidentally found a small chest in a destroyed room (despite the game promising that there's never anything interesting there). I had to crouch to get to it, and do a weird teleporting thing with boxes to get back.