The Čiperka mineral spring, which is one of the most famous acidulous waters of Slavkovský les (Slavkov Forest) may be found just beyond the border of the Karlovy Vary in the Plzeň Region. The acidulous water springs out at an elevation of 508 metres above sea level on the right side of the race of the former Lazurový mlýn (Lazurite Mill), approximately 100 metres before flowing into the Kosí potok (Blackbird Brook). It was declared a nature monument in 1995. Amphibolites with crystalline calcite enclosures (metamorphic rock formed by transformation of effusive rock at temperatures ranging from 450 to 750°C and at a pressure from 2 to 12 kbar) may be found on the site. The acidulous water was captured and made accessible to the public by the owner of the local electric power station, Oswald Hanika, in the early 20th century. Hanika ordered the building of an arbour over the spring and named it Hanika Quelle. The arbour is not standing on the site any more.
In the 1940’s, Kosí potok (Blackbird Brook) drove more than 35 mills, most of which are now only ruins. Apart from the Čiperka Spring, it was Hanika's electric power station where Oswald Hanika had been making three-phase current – a quite modern technology in the early 20th century. Hanika came from Dolní Kramolín and he tried connecting first electric generators in his father's mill. From 1898, he began with electrification of the region and he was one of the first to rebuild his mill into an electric power station. Hanika is merited for the electrification of the villages of Planá, Úšovice, Drmoul, Klimentov, Hleďsebe, Hamrníky, and Chodová Planá. Due to his siding with the Fascists in World War II, Oswald Hanika fled Bohemia before the end of the war. In the 1960’s, the station was nothing but a pile of ruins and today, we may only see its foundations occupied by a homeless man from Michalova Hora. The only preserved relic is Hanika's cross standing on the hillside by the road next to the ruins of the power station. There is a sign on the cross with a name and year: Theresie Hanika 1911.