This is the train through the core of the Earth that the movie Total Recall (2012), features. How is this supposed to work, the pressure at the core of the Earth is many, many times that at the surface and the temperature is 5430 °C, the temperature of the photosphere of the Sun. The outer core of the Earth is solid due to the immense pressure, it is a giant spinning core the size of Mars and made of iron, that is how we get our magnetic field that protects us from stellar radiation. How could they put a tunnel through the core if it is spinning? The inner core is about 1220 Kilometres in diameter and would be another obstacle to constructing our train tunnel since it is massively compressed and it is as hot as the Sun. What is the tunnel supposed to be made of? Unobtanium I suppose, but that old trope has no basis in reality, the tunnel would be facing seismic activity, the unimaginable pressures and the heat from underground. Everyone has seen National Geographic channel and the volcanoes spewing lava, that is a glimpse of what is underground.
How are they supposed to have built this in the first place, we can not even go 4 Kilometres underground without being uncomfortably hot, I can not imagine being 600 Kilometres down working on the tunnel. This concept is called a Gravity Train and has been investigated before, but no materials exist that could withstand the immense pressure. it is about 3,600,000 times the atmospheric pressure of the Earth at the core, possibly strong enough even in the mantle alone to crush Carbon into diamonds, therefore there is nothing in materials science we could build the tunnel out of that would withstand the conditions. What happened to the aircraft? Or the cruise ships?
Another good reference: http://www.math.purdue.edu/~eremenko/train.html