Defender of the Faith - Velen
Location: Road between Blackbough and Crow's Perch
Quest Giver: A lady standing on the road
Other Requirements: N/A
You can begin this quest at one of two different locations, the road between Blackbough and Crow's Perch (as seen in my screen shots) or at Duen Hen. Regardless of the location you start it at you'll have to visit both of these locations anyway in order to fix the shrine that was damaged there.
Once you fix each of these shrines people will typically start worshipping at them again, this is especially true for the Duen Hen location. At the final location you have to fix for this quest, in southern Velen by the Byways Signpost you'll find the group of bandits that have been destroying these shrines.
If you refuse to fight or kill the group of bandits that are damaging the shrines you will fail the quest. Beating them up or killing them will successfully complete the quest. According to the google there are no negative reprocussions on any future quests for taking these bandits out, so do as you please.