Back to Kaer Morhen
The Bastion is an observation tower located to the west of Kaer Morhen. When you get close to it this quest will be added to your journal.
Kill the Wraiths in the tower and then use your Magic Lamp to find out what happened here. There’s one place to use the lamp on the ground floor, three places on the second level and once place inside the ruined tower. The last image will show youa boy hiding there with his instructor.
Pick up the remains of the boy and bury him in the place marked out on the map. This completes the quest.