The Legend of Korra: Book 2 Episode 6 (Click to show)
And yup, I was thinking it was the big turtle at first too, but I don't remember there being other people on it.
GUYS WATCH THE SHOW, these spoilers are getting pesky xD I keep forgetting them till the last second <3
Warning: Spoiler! (Click to show)
Avatar Roku? I'm not actually sure what episode you guys are referring to. XD