I've read from this site about how to catch Regirock, Regice, Registeel, and Regigigas. I caught the original Regi-trio (thanks to LeafeonLol), and I've gotten the information about the conditions I need to face Regigigas, but one thing's confusing me: Island Cave, the location of Regigigas. Until recently, I never even heard of that location. I saw that some people have managed to get there, but I still don't know where it is, let alone how to get there. All help is appreciated.