One thing that comes to mind is 'explorable lore bits'. Stuff you need to go a bit out of your way to find, or solve a side puzzle to get to type of thing that gives lore you wouldn't otherwise have been given. For instance something like a diary in an abandoned cave from a guard that landed in there that might give a perspective that differs from the Fell Queen. Or a still semi sentient skull that fell through some crack and got stuck for centuries. Stuff like that?
Not all rewards need to be mechanical in nature.