There are many amazing railway tunnels all over the globe that are breathtakingly long--four of them are in Japan, two in China, and as this article by Railway Technology points out, there are three more in Europe that make for exciting train destinations in themselves. No matter where you're going on a railway journey in these lands, the ride itself is half the adventure.
"Lötschberg Base Tunnel, built through the Alps in Switzerland, is the third longest railway tunnel in the world. The 34.6km long tunnel allows passenger and freight trains operated by BLS on the Lötschberg line. The tunnel includes a non-ballasted track on which trains run at 250kmph." The Alps are great, but what about Spain? Passengers can start or finish in Madrid on the Guadarrama:
"Guadarrama is the longest twin-tube rail tunnel in Spain and fourth longest in the world. The 28.4km tunnel is dug through Sierra de Guadarrama mountain range for the high speed railway between Madrid and Valladolid. The two parallel tunnels are 30m apart, measured from their central axes."
There are many more of these "longest-ever" railway lines to explore--you can read all about them at the link below, but we can't finish here without mentioning one in South Korea---the Geumjeong tunnel, which the Railway Technology article points out is the 10th longest, part of a high speed rail line to Seoul. "The tunnel, bored through the Geumjeong Mountain, connects Nopo district with Busanjin station in Busan."
From Seoul to Madrid, there are many of these rail lines to explore and enjoy--even if you can only do it from a distance, these are impressive feats of design worth appreciating.