How bad is it? It's a "Beach Party" wannabe that fails. That's pretty grim.
Should you see it? Only if you're a huge fan of one of the stars.
Jack E. Leonard plays twins, one of whom is a cosmetics mogul who believes the fountain of youth is on an island off Florida (the other is a spy). Teenagers invade the island on a scavenger hunt. Phyllis Diller, Brian Donlevy and Jayne Mansfield make the least of their screen time. There's a lot of musical numbers, some of which aren't too bad. There's a mermaid. There's a dance called "The Turtle." There's a building set for destruction by air conditioning. There's about half a dozen intentional laughs.