Haha it's super easy to miss, it's like a '' hidden '' tunnel, there's a door to it behind rocks near the place you kill the dark elf with the shuriken.
The ring itself is super dark and on the ground near mushrooms, you need hawkeye to see it if you don't actually know it'S there.
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http://img.imgcake.com/cosplaygifer.gif
http://en.wikipedia.org/wiki/TORtanic