This is the forum for helping you out if you're stuck or if you want to discuss the nitty gritty details of the dungeons within Mount Grimrock. Warning: forum contains spoilers!
There's 3 switches, hit the one farthest away from your destination first
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If I can remember correctly... after triggering the trap, go south, look right and there's a hidden switch (high), then look back straight ahead, go all the way to the door and there's a hidden switch on each side there.
Poison triggers every time you step on the plate in the middle, I'm not 100% on what the door opening is based on (combination or speed, tho I can now open the doors within the space of one poison cloud)
If you wait for the poison to disperse you can then sleep to regain hp.
Give a shout if you still have trouble and I can tell you what works for me.