The Island is an jungle covered island north and east of Serenia. It maybe part of the Rocky Islets chain.
Background[]
The island was visited by the the Wanderer on his journey to save Priscilla in the North in the Unknown. It is the home of a pirate. The island and other nearby islands appears on one of Derek Karlavaegen's maps of the World of Daventry now north of the Great Mountains, rather than to the south of them (sent during the KQ5 era, although some of these may be based on the Rocky Islets seen in the distance from the sea).
The ocean surrounding the island was created by Harlin to divide Serenia into two landmasses, to create an obstacle against those who would try to defeat him. It lies roughly between the waters of the Western Sea and the Northern Sea. The waters of the Northern Sea continue to have magical properties to those who sail through it.
It is unclear if the island existed before Harlin used his powers, or if it still exists after the lands returned to their current state. Some maps do suggest a few small islands exist north of Serenia years later (though by this time, the northern half of Serenia including the Great Mountains had been restored to south of the islands).
This is one of the few areas known where a jungle exists, it may be possible this is where the golden lion was returned (besides Africa).
Behind the scenes[]
The exact name of the island is unknown, although it is described as having a jungle in the middle of the island in Wizard and the Princess and Adventure in Serenia. The game in general describes it as 'the island'.
In the game, the island is reached by sailing north. It is seen slightly east, and at that point can be reached by sailing east. It can be missed by sailing in any other direction.
This island and the rowboat used to reach inspired the inclusion of the Harpy Island in KQ5.
These islands appear to lie north of the polar regions (presumably the North Pole) where Icebella rules (assuming the polar regions are not separate from her region in the great mountains), if the pole is the most north one could go, then technically that should make everything around those points to the south. Thus the Island may technically be south of the north pole on the opposite side of the world (if the world was wrapped around a globe). At one time the great mountains lay north of it due to Harlin, thus at that time it would have been south of the polar regions but on the same hemisphere as the continent of Daventry. However compass notations still show the north to continue on into the northern Unknown.
Also its worth noting that the island itself may have been created/moved by Harlin as one of his obstacles to stop the 'wanderer'. But that doesn't mean that the island didn't exist before or after he was defeated but elsewhere. But it is clear that almost everything in the quest was part of Harlin's great spells.
This island could have been inspiration for the Green Isles as well, and the King's Quest Companion makes reference to missing or transmogrified "jungle islands' that sometimes appear near the islands.
This island and the pirate there upon may have been an influence for the beach in King's Quest 3 where the treasure was found, guarded by pirates. It might also be partial inspiration for the Hermit living on the beach in KQ5, and the whole 'hole in the boat' idea.
The treasure and x marking the spot, and treasure hidden in a cave maybe a reference for Trreasire Island novel.