Grimrock

No idea how big hint you want. =) In general, you should solve the puzzle involving wall signs in room before the grate, niches in pillars there, and scrolls found on the sublevel.

Yes, gold key is before lvl 4, you prolly missed it. Soooo, keep looking, have fun. =)

Figured that hiding your torch and putting room to darkness can reveal a loose soon-to-be-open walls. If there is a light source behind them, you can see them glowing a bit. That doesn't help you finding the switch, but tells the general direction where to look.

Level number is confusing sometimes, as, for example, people call the place where you fell from level 4's pits as both level 4, level 5, and even sublevel 4. I'd still call it 4, as this "sublevels" never do really connect with main area of next level. (judging on my 4 levels-deep experien...