thisispete
The Man Who Would Be King
One of the biggest problems in Civ III and prior incarnations is the length of time it takes for ships to get around the map. Canals are a real-life solution to this problem (which I had expected to be in Civ III when it was released). So maybe it can be a worker action that arises from an optional advancement in the late middle ages. There wouldn't be a movement bonus like roads or railways, but ships would be able to shorten their route.