I read it as sea mountains, although I brought up the leviathan-based sea creatures as base for their cities, too. Not really different from what Waertag did to sea dragons, only submerged most (if not all) of the time. In that case, we might have to ask us about their need to sleep, and how they pattern their sleep. Glorantha knows weird sleeping patterns, e.g. for the aldryami (brown elves hibernate, but don't sleep, for instance, while green elves generally follow the day/night cy