In 1935 the German newspaper Frankfurter Volksblatt published Grönhagen's article on Kalevala folklore. Reichsführer-SSHeinrich Himmler showed interest on his thoughts and asked Grönhagen to work for Ahnenerbe. He led a 1936 Finnish-German voyage through Karelia. This expedition mostly recorded pagan sorcerers and witches. In 1937 and 1938 Grönhagen made two more voyages to Karelia, alone this time. He also worked shortly as one of the institute's directors but was dismissed by professor Walter Wüst who considered Grönhagen incompetent.[2]
During World War II, the Nazi-minded Grönhagen worked for Finland's propaganda department and served as its military attaché in Berlin. He was arrested in Oslo 1945 and held in custody for two years. After his release Grönhagen was a businessman and emigrated to Greece in 1964. He first lived in Crete and later in Athens serving as the Master of the Christian Order Ordo Sancti Constantini Magni.[1]