I don't consider it a good sign when they deliberately put in these plot holes, just to make me want to watch the next season. I'm so fucking sick of this Lost style shit. Keep me watching because your telling a good story, not with these stupid plot carrots, that ultimately get hand waved away seasons later with something stupid, or never at all.
Diving into the planet part bothered me a lot, was that supposed to be the core of the planet? I kinda interpreted that as a giant pocket near mantle or something, it was far too small of an area. The upside down camera makes it appear they shot through other side, but that doesn't make sense for so many reasons. The exit was shorter than the entrance, depending on angle, following any of those holes out from that depth would take you to a completely different part of the planet, with drastically different distances (which it did)
Easier to accept that somehow the creature turned it around, or Mothers "maternal instinct" took over at last second, and use it as a flashback in S2. It was interesting those holes swiss cheesed the "ceiling" though, looked more like ancient boreholes from surface that mined out the pocket, and whoever made them delved too greedily & too deep.