Grimrock

I found what it opened, just had to lok around a bit more.
But what about those pits?

I've been to level 8 and found a note showing where the button is on level 7 but when I press it there is just a click and I can't see that anything has opened. Could you tell me what this button does. Also there is a room with three pits in the middle and a portal and corridor visible on the other ...

I've got a GTX 560Ti and I noticed its fans were running very fast. I checked and Legend of Grimrock is running at about 160 frames a second during gameplay - putting GPU usage above 98% and heating it to 94C. A simple framerate limit would be a welcome feature I feel. I'm using triple buffering now...