It's another Planet of the Apes/The Time Machine redux as a stuffy scientist (Peter Cushing) and a cowboy-inspired rich guy (Doug McClure) set off in an oversized drill/spaceship en route for the center of the earth. Of course, all kinds of creatures live there, namely large dodo-dinosaur hybrids, their monkey-pig underlings, and a humanoid race of slaves under their thumb. They even speak the Queen's English. While the fire effects are cool, the creatures are unilaterally awful. For 1976, an effects-driven film needs an awful lot more than plastic masks and stop-motion winking. Oh, and the script is lifeless, to boot.
Screaming the first time might be an issue if you can sit through this collaboration among Price, Lee, and Cushing, none of which do much with their roles. While some of the film's boundary-pushing (for 1969) moments of gore are spine-tingling (namely when a serial killer removes his own hand to escape a pair of cuffs). But this odd conflagration of mass murderer, scientific experimentation, and strange neo-Nazi group on the prowl stories just doesn't work. At all.