Would it be good to have random land treasure hunts similar to the random sea treasure hunts like shipwrecks, mysterious islands, etc ? (e.g. "Mysterious Cave", "Ancient Ruins" etc)
It seems like a decent idea in my opinion, especially now that 3 has no settlement ruins exploration at all. Not only would this add to the gameplay (and consistency) but it could also draw ai armies more away from settlements and facilitate more field battles.
Edit: although there is a mod
that technically does this and more, there are issues, and it would obviously be preferable to have a well designed and balanced system as part of the base game.