The unnamed island in the Southern Sea of Gielinor is visited during the Hunt for Red Raktuber quest. Players are left to die there by the leader of the malicious penguin organization, the KGP, Pescaling Pax, after they are caught infiltrating the Red Raktuber. While on the island players could not access their inventory or spellbook, so teleporting away by any means was impossible.
The island appeared to be deserted at first, but when exploring the island after the Red Raktuber had left, players will find Chuck disguised rather dubiously as a palm tree. When talking to Chuck, he explains that he was sent there to monitor the penguins by his employing organization, the PBJ. He will then take the player back to East Ardougne by letting them ride on his stomach.
Currently, there is no known way to return to this island.