Elden Ring’s Ring of Oath is an item that the game tells you is required to pass through a barrier in the Lake of Rot underground region. The problem with that is, the Ring of Oath doesn’t exist. In this Elden Ring Ring of Oath guide, we’ll tell you where to find the Dark Moon Ring — which is what the Ring of Oath is actually called.
Finding the Dark Moon Ring is part of Ranni’s questline — our full walkthrough of her quest can be found here.
Progress Ranni’s questline
Before you even need the Ring of Oath (aka, the Dark Moon Ring), you’ll need to have progressed Ranni’s questline quite a way. You’ll need to have already found Blaidd in the Siofra River region, defeated Starscourge Radahn, found the Fingerslayer Blade in Nokron, Eternal City, flipped the Carian Study Hall, traveled to the Ansel River via the Waygate at the top of Renna’s Rise (not Ranni’s Rise), and defeated the Baleful Shadow at the entrance to the Lake of Rot.
Defeating the Baleful Shadow will earn you the Discarded Palace Key. Examining the Discarded Place Key says it opens a chest “found in the Grand Library of Raya Lucaria with her mother Rennala.”
Open Rennala’s chest
You don’t technically have to have completed the Academy of Raya Lucaria prior to reaching this point, but if you haven’t done it yet, you’ll need to do it now. Once that’s all set, head to the Raya Lucaria Grand Library site of grace.
Open the locked chest off to Rennala’s left. Inside, you’ll find the Dark Moon Ring. This is the Ring of Oath — which is “symbolic of a cold oath” referenced in the ring’s description.
With the Dark Moon Ring in your inventory, that barrier will have disappeared and you’re free to continue on to the Astel, Naturalborn of the Void boss fight.