Hello,
after clearing out what I imagined to be the catacombs in the chatedral up north from mansfield, I thought that it be cool if you could find certain objects, maybe an old spellbook/scroll or something that can only be found at specific places. But it wouldn't stop there, enemies (especially named ones) would have the same idea as you, so they would actually have a reason behind travelling from their home.
Maybe some races/entities try to protect some old relics, so if you get them, you might be powerful but you now got a whole race of beings trying to hunt you down.
Another idea would be stuff like keys and such, that you have to find to go certain places, which would be carried around by enemies and other such that had the same idea. This would make every game very dynamic. Maybe some places can be world altering, so as soon someone reaches it you'd feel/notice it in the world and have a clue that someone did.
I don't know if any of these things would be possible to implement though.