I have seen several websites which list the recipe for the Cantlin Garden, but I haven't found anybody (or any thing) who makes it at all clear how to build one in the game. Magnus seems to give a slight clue, but nothing that clear.
Since the recipe calls for water blocks (spaces?), it does seem like there might be something wrong with the recipe, since Cantlin sits so high up. Is it possible that the town was raised up late in development (to restrict the height of rooms, perhaps), which rendered the recipe much more difficult to stumble upon from the clues?
I really want to know where it is, in-game, but if anyone knows about a hack or something that explains that this was accidentally left out, or that the prerequisites for the recipe to be revealed can never be fulfilled, please post that as an answer, too.