The door to the castle will open automatically, go inside. Talk to the person sitting in the chair. Ask "Etheral Ring" and then "vault." Next ask "Treasures"; "Protected"; and then say "Bye". Be careful now because the next area is almost impossible (I usually save.) There should be a door (like the other one) near the top of the room. Go in in combat mode. The statue will attack you kill it and get the key it was carying. Use the key on the door, and get the ring on the pedistal. Go back to Penumbra.