Steinbruch am Langen Köchel im Murnauer Moor, Quarry and geotope in Murnau am Staffelsee, Germany.

The Hartsteinwerk Werdenfels is a former quarry on the Lange Köchel, a roughly 120-metre-high glacial rounded hill on the western edge of the Murnauer Moos. From 1972 the working face was driven below ground level into a pit 40 metres deep, 50 metres wide and 1.1 kilometres long. The pit has since flooded completely and is now called Langer-Köchel-See, a groundwater-fed pond with no surface inlet or outlet, its surface at 628 m above sea level.

Quarrying began in the 1920s and continued through 2000, supplying material for rail and road construction across the region. After closure, the pit gradually filled with groundwater and rainwater, eventually forming a lake.

The hard rock mined here was sold under the trade name Glaukoquarzit. From 1967 large quantities of track ballast went to Munich's U-Bahn construction and the expansion of the S-Bahn network. The former canteen, a 1953 dining hall seating 300, could not be demolished because bats were found roosting in it; they still breed in the remaining front section in summer.

The location is easily reached on foot with marked trails around the quarry and lake. Spring through autumn is the best time to visit, when paths are dry and fully accessible.

The flooded pit is a Himmelsteich with no surface inlet or outlet, fed only by groundwater seepage and rain; its surface lies at 628 m above sea level. The quarry is registered by the Bavarian Environment Agency as geotope 180A004. The former canteen, a 1953 dining hall for 300, was saved from demolition because bats nest there in summer.