njvack wrote:I do rather like the idea of some vaults stopping exploration. It's probably appropriate for most vaults that aren't supposed to look just like the rest of the level.
Lots do this already. A few use a special marker property that can be placed on a (normal, non-monster) statue, and will give "a statue comes into view" (or some other message like this... I forget) when you autoexplore into them. Otherwise it's just a normal statue. This feature isn't used much though, and it's possibly worth using more. The whole purpose of it is to prevent autoexplore traps.
Another thing some vaults do is obstruct you with a plant or a mushroom, an obvious secret door, or some other feature like this. This method is a bit more overt but it can work well. Players have to "manually" enter the vault. Doors with warning prompts also serve this purpose, although I think prompts should be a last resort, since they're annoying if overused.
The other thing a lot of vaults do (which is really the most common method, and the best one to use when available) is to simply place weaker monsters somewhere close to the entrance part. Weak doesn't need to be trivial, just something that isn't OOD. This method can't really be used for crazy yiuf's hut, though.
I've gone a bit offtopic here, but I just wanted to point out that what you're suggesting is already in place for a lot of vaults, and crawl actually has several mechanisms for making it work.