Mystery on Monster Island(Misterio en la isla de los monstruos)

The story concerns a shipwrecked group who discover natural wonders and a gold treasure on a dangerous island populated by dinosaurs and living seaweed. Terence Stamp is the bad guy. Supposedly the most expensive film made in Spain to that point, it has an admittedly strong genre cast including Peter Cushing, Paul Naschy, and Ian Sera.