Phantom Island is the location of Black Ghost's base in the 1966 movie. It is a black stone island with a mountain that has caverns and rock formations which gives it the shape of a menacing skull.
The base is equipped with a laboratory where humans can be converted into cyborgs such as the 00 Cyborgs. The island is guarded by spy dolphins and equipped with an "ET Wave" transmitter, which the base can utilize to manipulate native undersea life such as a giant octopus to attack any who dare to come near the base. The island is also surrounded by robot sharks armed with guided underwater missiles to destroy intruders. The defenses on land include robotic cobras armed with flamethrowers, a spider robot and multiple armed guards.