This reminds me a lot of the other McClure films. They are what they are. Fine enough once, I guess. I won't repeat them.
Hulu has it online:
GoogleVideo has it online in 9 parts: part 1, part 2, part 3, part 4, part 5, part 6, part 7, part 8, part 9
Moria gives it a bad review but opens by explaining:
At the Earth's Core was the second in a trilogy of Edgar Rice Burroughs adaptations made by director Kevin Connor, producer John Dark, production company Amicus and star Doug McClure. The series began with The Land that Time Forgot (1974), continued with The People that Time Forgot (1977) and ended on the non-Burroughs adapted but Burroughs-styled Warlords of Atlantis (1978). All these films were lost world films set period, usually in the Victorian era.
1000 Misspent Hours says,
The main advantage At the Earth’s Core has over The Land that Time Forgot or The People that Time Forgot is lots of action.