Ask www.rmv.de how to get to train station Friedrichsdorf-Seulberg with S5 or use your navi if coming by car.
Map: https://goo.gl/maps/tQ2QvwgBHR3qjs1h9
The parking is at Seulberg Bahnhof in Herrenhofstraße/Neidhartingerstraße. It is east of the railway. If you end up on Römerstraße take the pedestrians bridge over the railway (typical hash marks may guide you).