The Star World is an area with what appears to be lanterns or possibly stars in the background as you walk up stairs leading towards the underwater world. The machine effect can be found in the constellation room here by going through a white door as you go up the pier.
The same creature is there, and usually he will take you back to the pier. Sometimes though (perhaps only after attacking the same passive kaibutsu which triggers the Kaibutsu Well event?), instead you will be taken to a slightly larger, inescapable hell room.