The site for the event, the Alte Rathaus, is located in the pedestrian zone of Miltenberg. For this reason, you should not drive directly up to the building (unless you wish to risk paying a 30 EUR fine). There is, however, a narrow lane that leads almost up to the pedestrian zone, putting you within a 30 meter walk of the front doors.
Free-of-charge parking spots are available on the access ramp to the neogothic Main Bridge (Mainbrücke), as well as on the ridge of the hill near the hostel (Burgweg). Otherwise, there are parking lots right there on the Main that cost 5 EUR per day, from 9:00-19:00 (seven days a week). After 19:00 parking in these lots is free-of-charge. There is also a big lot right across the street from the Church, on the Main, that is normally reserved for buses in tourist season, but is filled with cars in the off-season.