Retrieve the Stone Circle from Marvon Rivetseeker's workshop in Ratchet.
I once entered the foreboding chambers of the Sunken Temple. The evil in that place penetrates all that enter; I barely managed to find my way out, wading through the ooze that now covers the floors. All I can remember is stumbling through a large circular room, filled with serpent statues...
Recently, I discovered a round stone that appeared to have the same serpent symbol imprinted on it. I had it packed up and shipped to my workshop in Ratchet. Retrieve it, and I might be able to tell you more.