I guess if I had an unlimited amount of Marriott points, I'd probably start with the list of Ritzes that have made some of the more reputable "Top 100 in the world" list. Those properties are probably the least likely in the system to participate in aggressive mass market discounting. 250k gets you a week. (For this purpose, I assume we're looking at only the best of the Tier 2 hotels.)

I see two castles listed as options on the same page that shows the Ritz. I have no experience with either of them. It seems like there used to be a couple of other "unusual" partner properties in Asia, but I don't see them listed anymore.