I'm about to leave Bartz world and go to Galufs, and I've been told I wont be able to return. But there's a place near Cresent Island and the Airship base that I haven't explored yet, and I can't figure out how to get in. It's on a little Island and looks abit like the Ancient Library. I've tried landing the Airship on it, but nothing works.

I have look at a walkthrough, the frontsite's, but haven't noticed anything regarding that.