Erroneous Slovakia references aside, you can create a CivII oceanic railway by building a railway on land then cheating ('change terrain at cursor') and turning the square into ocean. I always do it when my empire reaches a certain size, and there are various places just gagging for a rail tunnel (eg. English Channel, Straits of Gibraltar, Straits of Hormuz, Siberia-Alaska.) I sometimes connect all the little Indonesian and Malay islands in a line to reach Australia. It's purely aesthetic though; you can't actually use the railways, they just add to the glory of your 'network.' A working rail tunnel feature would be very useful, especially since the Chunnel was built in the 1990s and the standard game runs to 2020!