Riesending cave, Cave system in Bischofswiesen, Germany

Riesending is a pit cave in the Untersberg massif above Bischofswiesen, Germany's longest and deepest known cave at 27.3 km surveyed length and 1149 m depth. From the entrance at 1843 m elevation, a series of shafts drops 450 m vertically to a horizontal level where a stream, the Sammler, flows through a narrow canyon. Below, branched horizontal passages and further shaft series descend to the deepest known point.

Cavers from Bad Cannstatt found the entrance shaft in autumn 1996 while exploring the high plateau above Bischofswiesen. Expeditions over the following years uncovered deeper sections of the system and gradually expanded the known network.

The name comes from Hermann Sommer's or Ulrich Meyer's astonished exclamation "Das ist ja ein Riesending!" ("That's a huge thing!") at the 1996 discovery. German cavers still quote the phrase when describing the find. The entrance lies in Flurnummer 94 of the Bischofswiesener Forst, and its location was kept secret until 2014.

Entry is closed by a steel grid with a lockable hatch under a municipal ordinance; the municipality of Bischofswiesen grants individual permits only for a legitimate interest and proven physical and technical suitability. The entrance lies on the karst plateau at 1843 m, and the cave floods heavily during snowmelt until late June and after storms, with ice and rockfall risk near the entrance.

From the entry point at 1843 meters (6047 feet) elevation, a sequence of vertical shafts drops 450 meters (1476 feet) straight down into the mountain without major interruption. The temperature throughout the entire cave system varies only between 1.5 and 5 degrees Celsius (35 to 41 degrees Fahrenheit) year-round, with constantly high humidity.