Alter Tiefer Fürstenstolln, Mining tunnel heritage site in Halsbrücke, Germany.

The Alter Tiefer Fürstenstolln is a tunnel system beneath the Freiberg region with a main passage about 10 kilometers long and side branches extending across a much larger underground network. The system connects several localities and continues to function partly today as a drainage network.

The tunnel was first documented in 1384 and evolved over five centuries into the backbone of water management for the Freiberg Mining District. Its role as a drainage system was essential to keep mines operating and to maintain regional stability.

The adit's oldest mouth, on the Freiberger Mulde about 500 m west of Tuttendorf, has a basket arch of gneiss with a sandstone keystone carved in relief with the Saxon coat of arms. It was called the "Nullpunktgrotte" because the 1850/1852 survey profile of the Freiberg district placed the zero point of its coordinate system here. The gate carries a crossed hammer and pick.

The tunnel system still operates today, channeling water into streams and rivers that contribute to local power generation. Visitors should know that this is an active water system and not all areas are freely accessible.

The adit mouth sits at 321.3 m above sea level and was called the "Nullpunktgrotte" because a 1850/1852 mine survey profile, 5.91 m long, placed the zero point of the whole Freiberg mining district here, at the system's central and most important adit. The sandstone keystone of the gneiss arch carries the Saxon coat of arms in relief.