The short version: Don't bother with it.
After really enjoying 20,000 Leagues Under the Sea, I went for some more Jules Verne and just finished with Journey to the Center of the Earth. I'm betting it was far more intriguing back when it was written, and I tried to keep that in context while reading it, but I just couldn't get there.
Even trying to imagine knowing nothing at all about how the Earth is made up and so leaving it to the book to carry me along on the adventure, there was just too much of it that had me asking questions to try and explain away much of the ridiculousness of the whole thing.
In the end, it was just too much.