What would happen if someone tried to do a real life version of Journey To The Center of The Earth?
If they weren't crushed by the material in the mantle and actually made it to the center of the earth, they would then implode due to their own weight.
You'd run out of cave.
Death in seven miles.
After a few miles they would die from the immense heat and pressure.
They would die. Certainly they never studied science in primary school.