There's a chest in the Cimmeria level 2 that cannot be opened unless you have Rogue level 7. Boccata is level 6 for me, and I've been wasting tons of time shooting arrows and battling the tough monsters on this level, but I'm not even sure his experience bar has gotten any closer to 7. I don't have this Arbalest, but I see a You Tube video that shows that's how he got to high enough level to pick the lock It's a chest like in the NE corner of the map, where the parth goes N and S, before turning W.

Anyone have any advice? From the You Tube video, looks like some very important stuff in that chest.

I thought you could even level Rogue skills by shooting at nothing, but heck, even shooting baddies seems to be doing nothing here.

There you go, that's your answer.