Adit Josef, Mining adit in Prostřední Lhota, Czech Republic.

Adit Josef is an underground tunnel system in Prostřední Lhota that runs through rock layers and exposes natural mineral deposits along its walls. The passages reveal the geological structure of the region and show how deep miners worked into the earth.

Gold was panned in the Čelinský stream during Celtic settlement in the 2nd–1st century BC. Mining peaked in the 14th and early 15th centuries, when quartz veins near Čelina were worked by tunnels and inclined shafts, with ore-crushing mills on the stream. The adit itself was driven in the 1980s during survey work; in 1989–1991, 19,500 tonnes of ore yielded 21.5 kg of gold.

The name Psí hory, "Dog Mountains", labels the gold district around Čelina and Mokrsko. Medieval miners crushed ore in mills on the Čelinský stream and kept a forge by the largest shaft; today the adit serves as a teaching site for ČVUT students and visiting groups.

Visitors should wear sturdy shoes and bring warm clothing, as the temperature underground stays cool year-round. Pay attention to wet areas and uneven ground surfaces as you move through the passages.

The adit is named after Saint Joseph, patron of miners, and its 1,835-metre backbone gallery links the Čelina and Mokrsko deposits. Between 1989 and 1991, 19,500 tonnes of ore from Čelina yielded just 21.5 kg of gold.