Children's or young adults novel about travelling in a vast flooded dungeon to reset a computer

I read this book back in the 1980s, and it was about a space ship crew (by the set up I'm sure it was a series, but I can't remember reading any other of the series) who happened upon a world that was in the midst of some crisis.

The only way to avert this crisis is to visit some sort of mythical overlord computer - who just happens to be within a vast underground flooded series of chambers filled with dangers etc.

So our heroes set off in some self propelling pods that their ship was carrying, on an underwater journey in which they were attacked by huge hostile sea creatures etc etc. They eventually reach the end of the tunnels and interact with the computer, averting the aforementioned crisis.