The Vatican City has the shortest national railway line in the world, but it almost had none at all.
The Roman Catholic church is sometimes a little… conservative, shall we say? Train lines were being constructed throughout Europe in the early to mid-19th century, but the pope at the time was not a fan. In fact, Gregory XVI blocked quite a few technological developments from the Papal States, including train lines and also gas lighting.
The pope was worried that this kind of technological progress would strengthen the middle class and thus undermine the authority of his rule. That fear was probably driven by the fact that the Catholics in France had just suffered a significant loss in the Second French Revolution. For the old guard, progress was risky.
Anyway, Gregory XVI famously condemned trains with the immortal phrase (and pun) “chemin de fer, chemin d’enfer.” Yup, “road of iron, road of hell.” It wasn’t until many years later that a train line into the Vatican City was finally completed. It’s the shortest national railway in the world: all of 300 metres in total, from the border with Italy to the sole station Stazione Vaticana. It’s mostly used for freight, with the very rare passenger service or ceremonial trip to mix it up.
[Thanks to Gareth E. for suggesting this topic.]