Icy mountain with surprisingly a dark type gym(who thought of that idea?). The gym is pretty hard if you don't have bug,fairy or fighting types. You battle Tess when you finish the gym and continue to Port Decca (and Regice). The whereabouts of Regigigas are go right after gym go right again and use pokemon who has rock climb right click then hold and move it, then click rocks also you will need girafig and dunsparce to enter.
when you go to the port decca route you gotta battle tess so u can go through