You shouldn't need the gps unit. The train station is the only one in Civ for that train. EVERYONE will be getting off there and it will be obvious. The port entrance is about a 4 block walk if you turn right upon leaving the train station. Again follow everyone else that has a suitcase. Once you get to the port entrance there are buses to take you to the ship (which is a long way with respect to the train station to port walk) You MIGHT be able to get a taxi if you don't wish to walk but its such a short trip most of the taxis don't want to be bothered. If you need more help than that, write back.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007