Since Cyllene's first (licit, chaperoned) visit to the surface, she's visited enough times to watch it get warmer, and colder, and warmer again, over the course of many (illicit, solo) trips.  She's gone close (though never that close) to the shore and watched the humans from afar, seen their strange, straight caves, and the coverings on their bodies, and the way they move about on the surface floor upright.

She's seen ships, the things humans use to make there be a surface floor on the ocean, one that moves around.  Humans swim, sometimes, but, as far as she can tell, never while as far away from land as ships go.

She's also seen ships below the surface, far below it.  But she's pretty sure that's not because the humans wanted them that way; the whole seafloor around them were filled with strange, seastar-configured skeletons.  She's pretty sure that swimming in the open ocean is for humans about as sure a death as wriggling her way far onto the surface land would be for her.

She's learned a lot about ships.  They are usually in this range of sizes, and sometimes they lower nets and catch fish in them.  (Cyllene has attempted to replicate nets, as if they were her idea, and got a pretty good start on it.  One of her sisters dismissed the idea as being human-like when shown a swatch of knotted seaweed, and Cyllene has to be intensely careful that no one suspect her of having upward sympathies.  She has a real net, human-made, in her secret grotto, and she can see that its purpose is the truly beautiful thing about it, but for now... it will remain solely decorative.  It has to.)  There tend to be kinds of ship, ones that do the fish-netting and ones that don't, really.

This ship, she thinks, is not one of the kind that does the fish-netting.  She hopes she's right, because as much as she wants to know about humans, she does want more to not be netted.

She approaches from underneath, runs her hands along its belly, and then - heads for the surface.