Gather a blood-scrawled note on a chest underground at Multiple locations ( -250, 1, -445 ) Copy/waypoint -250, 1, -445 or ( -255, 2, -409 ) Copy/waypoint -254.78, 2.38, -408.89. Can also spawn on the wooden desk in the middle of the lair.
Note: Each group member needs their own copy of the note. It takes about 5 minutes to spawn.