Interesting mix of live action footage and cartoon-like sets and props. Though this film is often categorized as an animated feature, it's more of a trompe l'oeil that wants you to believe you're watching an animated film. Can't say it's entirely successful (the real actors are a dead giveaway), but it makes for some rather creative-looking scenes.
The plot is an amalgam of Jules Verne influences. The core story (about an evil scientist building a weapon inside a volcano) is based on Verne's Facing the Flag, but Zeman doesn't mind borrowing royally from other Verne novels. If you're familiar with Verne's writings it's all a bit too random, but it's good enough for an adventure film.
Not everything works and some parts are really outdated, but overall the film has retained a certain charm because of Zeman's unique approach. It's really like nothing I'd ever seen before, which at this stage has become a pretty big plus. It's still way too clumsy for me to love it unconditionally, performances are basic, the execution's pretty childish and the effects can be pretty crummy, but at least it was memorable.