Mine Lochezen, Former limestone mining site in Walenstadt, Switzerland.

Mine Lochezen is a former limestone quarry on the north shore of Lake Walen beneath the Churfirsten mountains in eastern Switzerland. The site consists of a network of tunnels and caverns carved into the mountain, revealing different levels of extraction work.

The Marmorbrüche & Cementfabrik Wallenstadt was founded in 1861 with German mining engineer Heinrich Julius Tröger as a partner, extracting limestone and marble at Lochezen. Jacob Schmidheiny took over the majority in 1897, replaced the slide track with a brake incline and built a loading station and small harbour. The old kilns were demolished in 1919 after a 1914 landslide, and the works later traded as Cement- und Kalkfabrik Unterterzen AG.

The name "Kaliforni" for the northern shore of Lake Walen recalls the small-scale lime kilns once run here, since "Forni" means kilns. Cut marble blocks were rolled down a forest clearing to the lake, and the burnt lime was carried by rowing and sailing boats to Unterterzen for grinding.

The mine lies on the north shore of Lake Walen in the Walenstadt municipality, next to the former Seemühle works, and forms part of the Sardona Geopark. The tunnels and caverns are disused industrial workings with no visitor infrastructure, so the site is not set up for public access. The terrain above the shore is steep and the underground passages are unlit.

After mining ended, the site became a testing ground for rockfall protection nets starting in 2004, a facility unique in the world. The company Geobrugg-Fatzer AG uses the rock walls to test new protective equipment under real conditions.