The city of Heidelberg (HD) loves it's cult-related rituals. In fall, there is a Vampire ball where people dress in extravagant Vampire costumes (think "Interview with a Vampire" outfits). And in spring there is Walpurgisnächt, more commonly known as "witch night."
Wikipedia, this holiday originated by witches holding large celebrations with bonfires to celebrate the arrival of spring. Many in Heidelberg (HD) continue to celebrate the witch tradition.
On the top of the hill opposite of HD are monastery ruins and a Nazi amphitheatre. These were all built on top of druid ruins. On the last night in April, people (mostly hippies and students) hike the mountain - in darkness - and go to the ampitheatre. Hiking at night to the ampitheatre is no problem... there is a constant stream of people walking up the forest trails to the mountain (as one friend put it "follow the dreadlocks, drum beats, and smell of pot").