The Riddle of the Sands by Erskine Childers has some very good bits describing using the pre-1st world war railways around the N German coast - they are fundamental to the outcome too.
A seeming personal failing of mine: I find spy fiction -- generally reckoned
ipso facto highly exciting -- tedious in the extreme (the cognoscenti almost universally rave over John Le Carre -- what I tried of his stuff, bored me to tears). This very much went, with me, for
The Riddle of the Sands: I read it long ago -- managed to finish it -- but it was for me, basically soporific; and I have totally forgotten about the first-hand rail involvement therein, as above.
Perversely, one small trivial rail-related (though not intended, or referred to, thus by the author) matter stays with me from
Riddle of ... Earlyish in the book, the heroes -- in the course of their sailing round and about the coasts of Germany -- call in at what was then Sonderburg, on the Baltic near Flensburg: a town in an area formerly, and now once again, in Denmark; but at the time of the action of
Riddle of ... , in Germany -- with Germany having conquered in the mid-1860s, this southern part (with a minority of ethnically German inhabitants) of mainland Denmark; until its restoration to Denmark shortly after World War I -- Sonderburg becoming once again Sonderborg.
In the chapter on Denmark in Peter Allen and P.B. Whitehouse's book
Narrow Gauge Railways of Europe, published about 1960: the authors wax, in my opinion, more vitriolic than is called-for, about a policy employed by Germany re this part of the world during their 19th / early 20th century tenure of it: viz. the building therein, of extensive metre-gauge light railways abundantly provided with stations, in the area concerned, "as part of a plan to introduce as many Germans as possible into the area, these in the form of railwaymen [and by inference, their families]". (Sonderborg / Sonderburg was the focal point of one of these m/g systems.) Ethically dubious, one may reckon -- but would seem in my view: in comparison with the Nazis' excesses some decades later, extremely "weak sauce". Plus, if I had been a Dane living in that area in those times; would figure that the inauguration of all this delectable metre-gauge, would have evoked in me feelings of liking and reconciliation vis-a-vis the German occupiers, rather than resentment -- of course, in the eyes of normal folk, railway enthusiasts are somewhat funny in the head
. (The metre-gauge systems in this area, "North Schleswig", were all closed completely, or standard-gauged, in the course of the 1920s / 30s; not because of loathing on the part of the Danes -- a sensible people -- of "foul little Hun railways"; just the way of things throughout western Europe in those times, with road motor traffic in the ascendant.)