You’re looking for a small container with a logbook, pencil, and small Halloween themed trading items. Be careful crossing the busy street and watch for muggles in cars. Unscrew the lid to open. Re-screw the lid snugly to close leaving the container top side up and cover it well. Before you leave, take a moment to enjoy the view to the west.
More easily reached from other than the large parking lot to the north; but if you do start from there, take the walkway up.
V’z thneqrq ol avar erq rlrf.