Faraway Island

Faraway Island, Hoenn (from Pokemon Emerald).

How to get here. You need the Old Sea Map: beat the Kanto Champion, then talk to the scientist in the Experiment Room of the Pokemon Lab on Cinnabar Island and he gives it to you. From Kanto, talk to the sailor at the Vermilion City pier (the S.S. Anne must have left) and pick Faraway Island. From Hoenn, once you have also beaten the Hoenn Champion, show the map to the ferry attendant at the Lilycove City harbor. The sailor on the island takes you back to the port you left from.