it's the very thin, long canyon north of where you meet the guy north of where Chocobocolinaloola is when it's all dark... I threw Mog in there, and got it by accident. I was just throwing her for fun.
Its in 110AF you can see the treasure cube off the ledge just north of where the spotlight area is in 10AF you have to use the mog throw to get it but its very visible from the cliff its more straight then down.
PSN ID:Mr_Panda007 "I'm going to attempt a manual override on this wall." - Wheatley