I haven't been to any yet, but does it seem like there's some pattern to how they've been chosen so far? Maybe some kind of connection between them?

[It can't all just be random, can it? The lake, too— Aerith had spoken to Astoria briefly when it had appeared. The witch didn't seem to remember why she knew it, but it was there in her memory all the same, however vague. She felt some connection to it. Maybe it was the same for other worlds?]