Synthetic island created by and named after KAOS scientist Schwartz.
Initially discovered in the Caribbean by CONTROL agents Maxwell Smart and 99 while on their honeymoon, it is capable of being moved from place to place by means of a giant outboard motor at the back.
When not being used it is hidden among the Thousand Islands (count them next time).
[Episode #99: "Schwartz's Island".]
Reality Check: The name refers to the TV series Gilligan's Island and its creator Sherwood Schwartz. The episode was in fact filmed on the Gilligan's Island set.