So I am wondering if I am not giving enough credence to this picture in the Art book. At first it reminded me of a shrine puzzle, where all the orbs were in a similar cylinder container mixed up in differnet colors and I think you had to shake it to get the right orb out or something to that effect. But I think I found this picture on the actual map in another picture in the art book. I'm calling this the water gumball machine.
I'm pretty sure this is the same Water Gumball machine.
I find it strange that it is incased in water but found on the sky islands? So since I seem to be in the fast lane for speculation today, I am thinking that this might be another way to travel to certian underwater locations or at least help find their location. You put in your nickle or 5 rupees or what ever activates the Water gumball machine and one rolls out, down the plateform and breaks on the pedalstall.
Revealing a small mini world or a map location of a city, shrine or important location beneath the Sea in the center of the pedalstall. Like a mini 3D map or picture of it. It coud then appear on your map, what ever that ends up being at this point, and you would be able to either fast travel to it or at least know where to look for it.