Came to another slade fortress and decided to go straight to the bottom before going up. And in the chamber deep at the bottom of the magma sea, was nothing. Sorry Mon, your portal to hell is in another castle! Then I remembered the demon who made this fortress was already struck down. His whole empire had been taken by elves, including this fortress. No wonder why they weren't instantly hostile. So I went up to see the occupier.
When I reached the throne room, the administrator was there with the master, who was hostile to both of us, and an insurrection began. Neither of them were armed, so their fight consisted of the elf weakly pummeling the goblin while he ran until exhausted, then bled to death. I decided I wasn't satisfied with leaving the place to the elf, so I bashed his head in with my shield -- only 470 more kills like that to reach L+5 Misc Obj! The fortress became a ruin, and I wasn't able to claim it by demand alone. I'm not about to try to recruit supporters; there are only 13 goblins here, and they're spread out all over the pits.
The next Demon Master is a long way away, but at least he's alive, and his slab was the first I'd found. His empire is also one of the most successful, and the capital is home to 11139 goblins. It's the only goblin settlement I've seen with more gobs than trolls.