The Vatican Railway (Italian: Ferrovia Vaticana) was opened in 1934 to serve Vatican City and its only station, Vatican City (Città del Vaticano [tʃitˈta ddel vatiˈkaːno], or Stazione Vaticana [statˈtsjoːne vatiˈkaːna]). The main rail tracks are standard gauge and 300 metres (980 ft) long, with two freight sidings, making it the shortest national railway system in the world.[1] Access to the Italian rail network is over a viaduct to Roma San Pietro railway station, and is guaranteed by the Lateran Treaty dating from 1929. The tracks and station were constructed during the reign of Pope Pius XI, shortly after the treaty.
Beginning in 2015, one passenger service runs each Saturday morning with passengers for Castel Gandolfo. Most other rail traffic consists of inbound freight goods, although the railway has occasionally carried other passengers, usually for symbolic or ceremonial reasons.[2][3]
https://en.wikipedia.org/wiki/Vatican_Railway
I’m guessing they have tanker cars for holy water