Grimrock

Got a question about the Sunquazard Lake area. Put rocks on the pressure plates but don't get the hints on what to do next to open the underwater gate. Something about throwing a rock at night somewhere? Stuck here.

Where is that area? Do you mean the Palace area? I am at a point where I can't go anywhere. I finished the Palace in the graveyard but not the gated area outside it. The only places I can go is to the forest but can't open that door yet and I don't have the pendant to go further in that section.

Is there a hint somewhere to find the Spiritwalker pendant?