Ugh, I figured it was the snowballs because there were so many, but I broke them and got bored. I didn't notice a river. It is in the top left corner or the map. It beeps weirdly near the Hinox skeleton and the test of strength shrine. I've tried beating the Hinox, climbing up the mountain, and climbing down near the abyss but so far no luck. I did find one guardian and it killed 4 of my shields. Rude. I also found a shrine that apparently was a shrine quest I was ignoring. Gotta love completing quests without trying.