When the player characters travel to the Tower Valley setting, they’re leaving whatever campaign world that is the default for the Tainted Cosmos setting and entering a nether region that is less a location than a literary conceit. It is an eerie atmosphere evoked through wildly expressionistic visuals, florid dialogue, and a sometimes dreamlike logic.
Perhaps it doesn’t really exist on Caspia (or any known world), only in dreams. It is advised that the Game Master leave the question of whether Tower Valley is real or not open-ended, one which may never be answered. Keep it hazy, keep it dream-like.