Three Isle Path
Three Isle Path, 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.
Items
Hidden (use the Itemfinder or press A on the spot)
Given by people