Brain of Cthulhu
(Mono and Six got to the city by raft. I'm sure it's possible to do something similar for the Maw. Besides, I doubt people would be very happy if I just included the Maw or just included the locations from LNII)But the games doesn't actually mention how they travel between them. You're just implying that there is when we don't exactly know, unfortunately, we aren't the devs after all.