This quest can be obtained by entering a cave in the northwestern Kaer Morhen valley. It is found at the end of the road which leads northwest from Kaer Morhen proper. The cave was formerly used for the the Trial of the Grasses, before Kaer Morhen, but is now infested by monsters. In addition to killing the monsters, you can inspect various pieces of equipment and read a list of old witcher candidates who underwent the Trial. Exploring the cave sufficiently provides a reward of experience points.