I found the dispute of building the Panama canal confusing between multiple reports and tried it myself to see what is possible and what not. And ran into an accidental bug (screenshot below) So fort-fort is not possible due to restriction two forts can't be next to each other Citadel-citadel is not possible due to similar reason Fort-Citadel-Fort is possible but the ships refuse to enter the citadel. It appears that ships refuse to enter a hex more than a hex away from ocean. I don't know. I tried to make a Panama canal from Amsterdam to a nearby lake, you can see on the image what the idea was. Anyways here is the bug. For some reason the workboat can enter an inland hex next to a Fort, also on the image a funny boat between Busan and Amsterdam. Clearly a bug is not supposed to happen and is meaningless for a workboat to be there.