English:

You have choosen the Cache "Schwarze Eisenbahn" Good choice! Begin at the position:
N54° 47.590
E09° 26.001

Happy caching!

First you have to find out when the city of Flensburg was founded. Now subtract 1013 from the year in which you believe the city to have been founded, and call this number AB. You will get the next hint at the position with coordinates:
N54° 4B.5A3
E09° 25.B63

At this location you should first enjoy the stunning view over the city of Flensburg. While you are looking over the city, there should be a huge building behind you. Count the windows of the lowest floor of the left part of the building and then the windows of the highest floor of the right part of the building. Subtract the number of windows of the left part of the building from the number of windows of the right part of the building, and call the result CD. Now proceed to the following position:
N54° 4B.445
E09° CD.900
You should be able to park you car here.

Once you have arrived, you deserve a break. You ought to be in front of a building with pillars, count them. The total number of pillars, minus the sum of the digits of the year of foundation of the city of Flensburg, will give you a value E. Continue to the coordinates:
N5E° EB.195
E09° CD.6A5

At this location you will see, in an Easterly direction, not far from the path, a wooden sign. Count the number of times ,L' (the letter) appears on this sign, and call this F. Now continue to:
NFE° EB.1EB
E09° CD.F9C

At this point you will see, to the left of the path, a raised hide which stands on four steps. On the underside of this raised hide you will find the next position on the beams.

Here you will find a second sign, indicating a historic place, supported by two posts. You will find the next coordinates written on the back of the sign.

When you have reached the point, you can see a sign, to the left of the footpath, next to the railway. It shows 4 numbers. Begin on the upper left side, and read these numbers, calling them JHIG respectively. The Cache is placed at the position:
NFE° EB.CAF
E09° CC.BFH