Which castle can’t be taken by a Necropolis on day 111?

He didn't explain it—I figured it out myself—external dwellings of high-level troops with a castle by the end of the week.

But how did he figure that out on 111? On a fix, everything is clear: the map is known and all battles are practiced, but what's the point on a random map? Besides, you actually have to find an external dwelling. I tried that once on Jebus Cross. On 113, I had to take RE and decided it was better to just fight through everything normally. Simple gremlins rule in same-faction mirrors and Dragon Utopia, nowhere else.