Cave In
This building was a former prison until the cave in. You see, prisons aren't built very carefully, they just try to get them done fast enough to stuff people in there. So while you can tell this was once a building, it definitely isn't a prison anymore, since the whole thing caved in.
Picture the cave in in your mind. Can you see all the little prisoners and guards being squished as the building tumbles down around them? Oh no!
かん
おちい, おとしい
None
You keep picturing the cave in and you see Genghis Khan (かん) climbing over the rubble. He's the one who took down this prison! And he's coming for your town next!
Genghis Khan is all about being smart and using better tactics. In this case, why fight a bunch of guards and prisoners when you can just cause a cave in and win immediately? The ol' Khan cave in, a classic war maneuver.