Okay, you're looking for the Ring in Darkness (Ring of the Wind), yes? You're not supposed to go in the 'Y place' (Yasinimarus). The place you're looking for is Nammu, which is on the mainland. To get there, go to Yasinimarus, but don't go in (and yeah, hide from flame atronachs! I really hate them
). Now go northwest from there to the mainland and cross some hills. Nammu is next to a little pond, but fairly near the coast so if you go too far inland, you've gone, well, too far
. It's not a daedric or dwemer ruin, it's a cave with one of those wooden doors.
Did you talk to the Dunmer savant and scout? They should have told you you were looking for somewhere named Nammu, not Yasinimarus.