Have you ever heard of the Bloody Verdict of Verden (search Massacre of Verden on Wikipedia)? It’s cited as the single most important event in stamping out traditional Germanic paganism / shamanism. Thousands of spiritual leaders were executed by the Christian emperor Charlemagne backed by the bloody Holy Roman Empire. It’s really tragic.
Another interesting source could be the book “Dreamtime : Regarding the Boundary Between Wilderness and Civilization” by Hans Peter Duerr. Maybe I’m just imagining things because the author’s name is German, but I believe he talks a lot about traditional German (or if not specifically German than European in general) healers and spiritual practitioners. It’s a fantastic, utterly astounding and intelligent treatise on natural spirituality vs. civilized culture. Reading it will definitely give you some perspective on the lost traditions lying beneath the concrete and corn rows.
Any sagas would be a good place to look too.
The Sacred Texts archive has these two things. First, a long first-hand description of the ancient German people written in the first century by Tacitus, a Roman scribe, which will give you a good view of their traditions though it’s from an imperial source and he substitutes Roman deities for indigenous ones (though you can infer the universal characteristics being worshiped). That’s here:
http://www.sacred-texts.com/cla/tac/g01000.htm
Secondly, a list w/ descriptions of the festivals of West Germany, laying out how they worshiped the cycles of the year and other special events, highlighting pagan roots and mystic symbolism (as you could with American holidays such as Christmas, a mockery of the pagan Yule, the Darkness Before the Dawn–the Christmas Tree a modern version of “bringing in the greens”, another Euro-pagan tradition–see “The Golden Bough” for an exhaustive exploration of holidays and their traditional roots). That article, Festivals of Western Germany, is here:
http://www.sacred-texts.com/etc/fwe/fwe06.htm
Hope that helps! Dig those roots!