Two Island

Two Island, Kanto and the Sevii Islands (from Pokemon FireRed).

How to get here. Needs the Tri-Pass. Beat Blaine in the Cinnabar Island Gym; Bill then takes you to One Island, where Celio gives you the Tri-Pass. With it, the Seagallop at the Vermilion City pier (the man at the gate at its end) sails to One, Two and Three Island.