Science fiction has long tried to explain the mysteries found at the centre of the Earth, indeed so little is known about what goes on beneath our feet that many scientists are starting to look inwards, not outwards.
Helping to make that science accessible is the age old question that has all of us scratching our heads: If we dug a tunnel from one end to the other, how long would it take us to fall?
The answer it turns out will almost certainly surprise you.