Behind Drei-Annen-Hohne the line runs steeply downhill and the railway reaches the 58 m long tunnel below the "Thumkuhlenkopf". It is the only tunnel in the Harz Narrow Gauge Railway network. On emerging from the tunnel Wernigerode Castle can soon be seen in the distance. In the vicinity of the station at "Steinerne Renne" (km 54.5) the line enters one of the HSB's tightest curves with a 60-metre radius, before reaching the station of Wernigerode-Hasserode (km 56.3). The next stations en route are "Hochschule Harz" halt (formerly "Wernigerode-Kirchstraße") and "Westerntor" station (where the Wernigerode-Westerntor Bahnbetriebswerk is found) at Wernigerode. Its terminus is the station at Wernigerode (km 60.5). The first section of the Trans-Harz Railway to go into service was the line from Nordhausen to Ilfeld on 12 July 1897. On 7 February 1898 it was extended as far as Netzkater and on 15 September that year to Benneckenstein. From the north the section Wernigerode to Drei-Annen-Hohne was completed on 20 June 1898. The remaining section between Drei-Annen-Hohne and Benneckenstein was finally opened on 27 March 1899 along with the line up to the Brocken, the highest peak in the Harz mountains. The original operating company was the Nordhausen-Wernigerode Railway Company. After the compulsory acquisition of the line in 1949, the East German Deutsche Reichsbahn ran it until 1993. From 1899 the Trans-Harz Railway crossed another metre gauge line at Sorge. This other line was operated by the South Harz Railway Company (SHE) and ran from Walkenried via Brunnenbachsmühle and Sorge to Tanne. A link line, initially just for passenger trains, was laid in 1913. In 1945 services between Sorge and Brunnenbachsmühle were closed, because this section crossed the Inner German Border. The section from Sorge to Tanne continued to be worked until 1958. The tracks were left on the border bridge until the fall of the Berlin Wall in 1989.