Oh, good thread!
Would suggest something like Red Dead Redemption bounty hunt posters but as a notice board with different contract posters each day of creatures.
Such as Drowners, Harpies, ect. Different posters based on each major or small village. Small villages could have different types of creatures say drowners as the smaller villagers.
Example of discription of one poster could be.
"Attention, to any traveler, their has been sightings of drowners closer to the village then we dare like for, the imperial watch seems to think it's better to remove their dead further from the main city but it's us lowly folk that has to suffer. Please track & kill this vile creatures & bring back proof of your deeds & you'll be rewarded."
Now when you go back there could be set places you could go, such as the "mayors" hut or part of the village or city such as a guard outpost? For reward.
Villagers could give you bushels 'to top up your potions, alcohol? & Cities can afford coin or other, one free repair from a blacksmith?
There could also be extended version of these contracts return location. Such as, for Novigrad, Guard outpost to return there, another location could be the fishing market or doc deeper in novi grad. To give the feeling these 'random encounters' are effecting all the place as per norm in The Witcher world.
This could be random each day & the creature time & place random aswell, have the contracts have a small discription of what the creature maybe, lives near water last scene location, & have few details along the way so you could feel like you are tracking.
Small options of tracks random dispersed based on random contract.
Have this free DLC later down the track (probably 6 months) so it adds to the longevity of the Witcher 3.
Will add more detail little later when it comes to mind.