An invisible political boundary (the dashed line on a map) can prove a greater obstacle than a towering mountain range when it comes to impeding railway operations.
In mid-April, my Irish friends and I explored the Gotthard Pass, where massive investment will soon make the old line over the mountain redundant as the new 35.5 mile Basistunnel beneath the Alps will divert most of the through traffic.
A week later I was exploring the border area between northern France and Belgian Wallonia with Mauno Pajunen.
Generally speaking SNCB (Belgian National Railways) provides an excellent service across Belgium, with most stations seeing at least an hourly passenger service and many lines operating with an even greater frequency.
It had been many years since you could take a train directly from Mons to Valencienes.
In theory, you can ride from Brussels to Valenciennes via a change of trains at Lille, but this is the long way around and impractical for regular travelers.
The end of the line for SNCB! (but the tracks once continued into France.)