Hidden islands are islands that are difficult to find. Fictional hidden islands are often shrouded in both mystery and mist. They are likely unmapped and in narrative worlds often are only found after a crew becomes lost at sea due to a storm. They may exist in the center of perpetual fogs, storms, whirlpools, or treacherous waters. Hidden islands may also be kept hidden by a person or group of peoples for reasons of their own. Hidden islands may contain ancient civilizations, long-thought extinct animals, behemoths & leviathans, or ruins from another age. They may be the sites of wonderful relics, temples, or powerful magics. They may host secret laboratories, military bases, super villain lairs, or bunkers. There may be skull rocks on them.