This film is extremely rare. I watched it on Danish tv when I was kid - something like 26 years ago! - and have been hunting it ever since. Finally I tracked down a German rental tape, but apparently no English language video exists?? THE MYSTERIOUS ISLAND OF CAPTAIN NEMO stays fairly close to the source (in the book Jupiter is an orangutan, not a chimpanzee, ok, that's a very minor detail). However the film adds som weird sci-fi touches. Back then I was very fascinated by the remote rayguns with which Captain Nemo (Omar Sharif!) protects his realm, while today they admittedly look suspiciously like car lights on sticks. But the film is still great fun.
Review of The Mysterious Island of Captain Nemo
