Throttólf wants you to find the top of the waterfall inside the Brackwater and see if you can recover the treasure Ógur mentioned.
'I am glad you're here, ${PLAYER}. My party became separated shortly after we entered the Brackwater, and I have not yet been able to regroup with them.
'I almost found my friend Ógur, however; he seems to have made it to the top of the waterfall down this passage, somehow, and I heard him shouting about some sort of strongbox that he found at the top of it. I fear that the cave-lizards must have been drawn by the sound of his shouting, for I have not heard from him since.
'If you can find the same passages he used to come to the top of the waterfall, however, you might be able to find the treasure of which he spoke! I will reward you handsomely for news of it, ${PLAYER}, and for news of Ógur's fate as well, of course.'
The treasure of which Ógur spoke may be at the top of the waterfall deep within the cavern known as the Brackwater.
Throttólf has asked you to find the passages leading to the top of the waterfall so you can investigate the possibility that some treasure might be found there.
Throttólf is in the cave called the Brackwater, near the entrance, down a passage from the base of the waterfall.
You found the strongbox at the top of the waterfall, but whatever treasure it might once have contained has long since fallen into dust. You should return to Throttólf with these tidings.