Many years ago, I proposed to Michael Linden, to do a SLRR underwater tunnel connection between the Heterocera Atoll (Cecropia region) and Bay City (Manyiminya region).
At that time, there was none in SL and Michael intended to start a ferry between the 2 regions, to transport trains between the 2 Continents. But he never had time to put into production that ferry, the trains in Mainland have now several cars and by now, we have several BSLRR tunnels in Bellisseria, they are lovely, proving that the idea has "legs to run".
I think it's time to revive the original idea.