I live in a rural area. Many years ago we had friends over, their youngest girl was around 4-5 at the time. Walking from the shed to the house she stopped & was in awe looking at the ground saying "oh my gosh, there are so many people living there! Do you see them? So many people" I have read about those who live within the Earth ~ would love to learn more about it. In saying that though, we're in a minig area, closet one appparently 15kms away - no doubt tunnels would be extensive. Their main concern with bushfires last year were the tunnels because they connect so far underground.