German Narrow Gauge?

This December the history department at the high school I teach at is taking a group of students on a WW II History tour in Western Europe. If having an all expense paid trip during Christmas break wasn't good enough, we will finish the trip with about one day or half a day in Berlin to do what we want, vs what the tour company wants us to do.

Are there any German narrow gauge railroads near Berlin that would be easy to get to, possibly with students in tow? Might as well take full advantage of being there!

If no narrow gauge, I would settle for some standard gauge steam.

Any suggestions would be greatly appreciated.

Kevin