Blackthorn’s Castle was a planned location within Ultima Forever more or less from the game’s inception. In fact, Mythic’s idea for his inclusion in the game was to show the first hints of his transition from an apparently trusted advisor of Lord British (and, subsequently, Lady British) to the Shadowlord-corrupted tyrant the Avatar faced in Ultima 5. Here’s what it looked like in the PC alpha test of the game:

And here’s how it appears now, in the iOS version of the game:

As you can see, it is more or less unchanged. And unfortunately, it has always been inaccessible to players, and always will be now. Which is a pity, because (as is the case with much of Ultima Forever), this was an area of the game that featured some significantly beautiful artwork…the only surviving piece of which can be seen above.