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!
3 floor switches, 2 of which you use to put a spider on a middle one in between bars. I do that and I even press the button on the wall to the left if you are looking at the spider but nothing. None of the doors up top open this puzzle is just... my brain hurts soooo bad.
So I figured out that if you drop items down the two slots with the hanging lanterns and presses the wall switch the back area opens up to get the helmet but once again no progress further on.