not to sure where exactly but the place where it is but the place where you activated the water wheels.... there are two sub lands, sunken ruins and cloudy domain. Go to area where you have to activate those electricity ships and you should find a platform to go into the cloudy domain
no thats not right its in the water world (i forget what its called.) and you go to where blink the mole is and turn right and go for awhile and eventually you will get to this place where there is moneybags and some things you need to activate with electric breath and if you fly straight across from moneybags there will be this platform and you push triangle and it will go up to cloudy domain.
Please tell me how
If I'm where you are thinking of, you need to get underwater breath (squirting), if I remember right you will need to get enough dark gems to get you into the cave with the tentacles and defeat ineptune. This will give you the water breath to go back and turn the wheel.