My guess is that ships and other sea-going vessels will be the "big huge feature" he's talking about. When entering The Swamp (for instance) skeleton characters will go on about how the place was a huge port city once and say something to the effect of "people loved their boats back then."
The following was taken taken from the FCS, under Swamp biome entry:
Skeleton:' '"Used to be a great port city around here..."
Human: "A PORT? In a swamp? What was it for, flying swamp boats?"
S: "It was a long time ago, the water level was a few hundred meters higher back then."
Interjector: "I don't know what a meter is, but that sounds like a lot" [sic]
S: "Relatively, yes. People loved their boats back then."
H: "Are you saying the whole world was flooded?"
S: "Relatively, yes. People loved their boats back then."
H: "Every time you talk it just fills my head with questions."
'I: '"What's a boat?"