20th Century Fox's attempt to repeat the success of Journey to the Center of the Earth with another respected English character actor and occasional star in the lead (Claude Rains) plus some handsome lunks under contract to the studio in support (David Hedison, Jill St John, Michael Rennie), in addition to character actors, a comic animal and special effects.
Claude Rains has a lot of fun with dyed red hair and beard - I think he could have gone even more hammier. Jill St John later grew into an okay actor but she's dreadful here - she copped it for wearing tight pink pants but that's not the problem, it's her acting. Michael Rennie is the big game hunter who is along on the ride for back story; there's also journalist David Hedison, St John's brother Ray Stricklyn (who basically has "surplus to requirements character ready to die" tattooed on his head... only he lives!), Fernando Lamas as a suave (surprise!) pilot; Richard Haydn as a rival professor; Jay Novello as a comic relief scaredy-cat. Throw in a beautiful native girl, a long lost previous explorer who's discovered (wasn't this in The Land That Time Forgot?) and you've got an awfully big cast. Too big really.
I guess they wanted Rennie and Hedison to figh over St John and Haydn and Rains to fight with each other and Stricklyn to romance a native girl, and Lamas to turn traitor... but honestly some of these roles could have been doubled up.
I didn't mind the back story about the previous expedition although the connection of the survivors felt tenuous - I wish Rennie had had more a personal link than "I was going to be their guide". The romance between Stricklyn and the native girl is really under-developed; ditto that between St John and Hedison.
It lacks a sense of wonder and adventure - I think setting it in the present day was a mistake, these things always feel more "real" set in the past. The special effects aren't that great either - we never really get decent dinosaur action - and instead of stop motion action they use enlarged lizards. The movie feels like it was made for a million dollars too little or something.
Irin Allen fans will enjoy the scene of the cast creeping along a narrow passage way avoiding fire - which would pop up in The Poseidon Adventure and When Time Ran Out. Kids will probably like it. Its in colour and is harmless.