SERIOUS SPOILERS FOLLOW
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The funniest part about it is that they are hinting at something huge with the quickly revealed and unexplained society of clones that is secretly working below the surface of the Earth. (His name was "Olsen", right?) I mean, not only can they travel in time and are clones, but they are not afraid of death. Olsen sets off the one explosion with no concern. He either knew he had to die there, ala the cyclops from "Krull," or death was no change for him. Was each Olsen just part of a community consciousness or did they reincarnate somehow? What in the heck were they doing down there? There had to be a reason for the city or laboratory.
Last, but not least, why did they want Lindenbrock to discover the world that was hidden deep under the Earth's crust? A disguised Olsen sold the book to Lindenbrock in the first place, so what was the reason?
In its last ten minutes, that movie creates more questions than it answers in the other eighty. When you said you kept falling asleep, I despaired, because you have to get all the way to the end for the payoff. Then, pow, crazy time traveling clones plot out of nowhere and THE END.
It's funny, because I was sitting watching the last half hour of the movie, my mind kind of on autopilot and then BAM. I sat up, thought to myself, "Did I just see what I think I saw?" and had to rewind. For a minute I thought I had fallen asleep again and missed something vital, but nope. Just that sudden shot of an underground high tech city of clones, right out of nowhere. I also wondered why Olsen left that doohickey to the Professor, especially if it was capable of transporting people to the moon. Talk about irresponsible temporal travel.