Markus-Semmler-Stolln (adit) was started in 1503 as the main drainage adit of Schneeberg’s silver and cobalt mines. It was enlarged to become the principal adit in the Schlema-Hartenstein District and since 1946 it served as the main drainage adit of the Uranium Mining Landscape, its total catchment lengths totalling over 220 km. It is Germany’s longest serving adit in continuous function, and its portal is included in the nominated property.