Info on the tunnel:
Mercury; Created in the middle of the 18th century under the name Grube Bruderhorn, from 1773 a new beginning under the name Palatinate Muth; provisional end of operations around 1800; subsequently, until 1846, multiple attempts and climbs without funding; renewed start of operations in 1879 under the name of pit unit (change to the mines Archangel, Palatinate Hope and Palatinate Courage), shortly afterwards end of operation without renewed funding; The mine was opened again in 1937, this time with the aim of extracting iron ore, but the work that had been going on until 1941 was unsuccessful due to the poor quality of the ore.
Mine building with three floors (as of 1797): the upper one was opened before 1797, the middle one was built 18 m lower, 108 m long, at 60 m depth the lower floor with a tunnel length of 404 m is from the lower one In addition, a 24-meter-deep sink was sunk.
Source: Wikipedia