Bürgermeisterloch (Schartentor) on Mönchsberg
The Schartentor is a little gate or passageway through city walls on the Mönchsberg Hill; in fact, it links the Mönchsberg with the Festungsberg, the latter being the hill that carries the Festung Hohensalzburg (aka Salzburg Castle). The name Schartentor is not commonly used in Salzburg (in fact, it hasn′t come to the attention of the Visit-Salzburg.net editorial team that this was the official name until we wrote this article). The passage is locally known as "Bürgermeisterloch", meaning "mayor′s hole".
The Bürgermeisterloch was built in 1863, at a time when many walls and fortifications of Salzburg were demolished. It is named after Heinrich Ritter von Mertens (1811 to 1872), the mayor of Salzburg between 1861 and 1872. He owned the Villa Bertha in the Nonntal and therefore, the Bürgermeisterloch came in rather handily for him and his way to the Altstadt.
The Hans-Sedlmayr-Weg road passes the Bürgermeisterloch coming from the Nonntal side. Keep on going and you will get to the Toscanini-Hof and the Felsenreitschule. You can also take the Oskar-Kokoschka-Weg to get to the Fortress. Near the Bürgermeisterloch there are several old farmhouses and manors worth a closer look. You can also go northwards for extended walks on the Mönchsberg itself, for which the Bürgermeisterloch is a good starting point.
SalzburgWiki on the Bürgermeisterloch (German, but with picture)