Dr. Michael Holtkamp Micha. Economist, owner of Graukaue, working mine owner. Graukaue | Michael Holtkamp (Cover) Graukaue | Michael Holtkamp (Cover) E-mail micha@graukaue.ruhr E-mail micha@graukaue.ruhr PGP key PGP key Website en.holtkamp.ruhr Website en.holtkamp.ruhr Instagram @michamaenneken Instagram @michamaenneken Mastodon @michamaenneken@ruhr.social Mastodon @michamaenneken@ruhr.social ResearchGate Michael Holtkamp ResearchGate Michael Holtkamp Telegram @michamaenneken Telegram @michamaenneken X @michamaenneken X @michamaenneken Tweets by michamaenneken Newest episodes No episodes with this miner Deutsch Deutsch graukaue.ruhr/kumpel/micha