99.7234 left Thumkuhlenkopf Tunnel with train 8933, the 09:40 Wernigerode - Brocken passenger, on 17 February 2017.
This is the only tunnel on the Harz system and is only 70m long. It takes the railway under a ridge as it comes out of the Thumkuhlental horseshoe curve and rejoins Drängetal for the remainder of the climb to Drei Annen Hohne.