Hmmm guys i found something pretty weird.
While walking around that huge rock where adamantoise is supposed to be (Yes, i was trying to spot him lol), and precisely on the west side, suddenly the game played that strange music that you can also hear when you are near the bandersnatch.
So i thought that i may have been getting closer to a big boss (adamantoise, again). Infact Noctis began walking as if he was in a dungeon (you know, sort of cautious pose).
Also i found a hole near the place where the music began playing. I think you can get through it cos its sufficely big, but i couldnt find a way to get in...
Anyway i think you can reach adamantoise by entering in that hole.
Just a theory :3