The King Kong story, like The Lost World, The Land that Time Forgot, The Last Dinosaur, Marvel’s Savage Land, et al., owes a creative debt to Jules Verne’s 1864 novel Journey to the Center of the Earth, which really popularized the whole “modern man goes to a primitive place full of prehistoric, dangerous creatures” subgenre. That book has been adapted for film countless times, but of interest today is the 1977 Spanish version Viaje al centro de la Tierra (AKA Where Time Began), for the reason that it’s arguably a piece of 70s-era Kongsploitation that flew under the radar compared to the higher-profile likes of A*P*E, Mighty Peking Man, Queen Kong, and Yeti.
As an adaptation of the novel, this version is nigh-perfect, sticking closer to the source material than any of the others I have seen. Yes, the book does feature a giant proto-humanoid near the end, so any accusations of this being Kong-inspired are simply a factor of timing, even if this big ape resembles the 76 Kong more than some of the undeniable knockoffs do. Admittedly, the big special effects sequences are sparse and not quite up to par with the time the film was made, but watching it in retrospect (when you can pretend it’s from a decade or two prior), it has its own quaint charm, and certainly beats out a solid handful of other Journey to the Center of the Earth adaptations.
The film got a US DVD release in the mid-2000s courtesy of Media Blasters, which fans of kaiju movies know means that it’ll be difficult to track down. I do see another release on Amazon, but since the website’s review algorithm tends to mash disparate editions together, it looks like that could be a total crapshoot (some report no problems, some report 45 minutes of footage cut, some say that it’s a totally different adaptation from the 80s!). One extra feature on the MB disc is a trailer for Legend of Dinosaurs and Monster Birds, from the same year, which admittedly makes this film look alright in comparison.