From Director Juan Piquer Simon, who created Supersonic Man.
And staring Peter Cushing and Terence Stamp.
But neither of them play the lead. Instead it features Ian Sera.
He plays a Teenage Boy who end up on a island with Monsters and Evil men.
It claims to be based on a Jules Verne Story but once you see the movie, you realize that claim is a insult to Verne.

And did I mention the Monsters? they make the creatures in "Land that Time Forgot" look like the work of Ray Harryhausen . They are bad.