Grimrock

The button I'm referring to is on a ruin wall in the northwest-ish area of the map. The button causes an underwater light bridge to form over a three-square pit area that contains some items. I don't understand what the purpose of activating the light bridge is? It is not activated by default, and shouldn't be such that you can get down into the pit to get the items inside. Activating the light bridge just seems to seal off the pit, but for what purpose? I've examined the walls above the pit after activating the light bridge but found nothing.

that light bridge is on by default and the button toggles it off/on/off/on ..
prolly it was just one click too much