Mundane Ring

The Mundane Ring is one of the most powerful magical items in the game. Available to characters at higher levels, it is not found at any fixed location but will appear randomly once you have reached a certain level. In combination with the Breton race's 50% magical resistance, this ring can make you immune to all spells.

Raven Camoran will have one in Main Quest: Paradise if you are level 22 or higher. Also, in the meeting part of Path of Dawn, It is possible to meet Raven and grab this ring. It is not known of the level for this to happen, But assume 22+ aswell.