"White Crystals" in Dying Light 2

In order to start this quest, you must complete the "A Place I Call Home" story mission. As a reward, you will receive 1500 combat and parkour points, 3 regenerations and 500 coins.

First, talk to Pierre in the smokehouse west of the Nut Windmill (or something like that). Head to the dark area in the Muddy Grounds that the marker points to. Get inside the building and kill six renegades. Three are below, three more are above, where you can get through the elevator shaft. After killing the renegades, visit the room opposite the elevator shaft (it will open when everyone is dead). Go inside and talk to Rook and Pierre who appears.