Get a few bits of wood, some pram wheels and a big hill. With a helping of gravity, you can satisfy the big kid in you by hurtling downhill with only your engineering skills and wits to see you to the bottom in one piece.
A soap box cart originates from the good old days when kids used to get a wooden soap box crate, stick some pram wheels on and race them down hills. Today, amateurs, kids and professional engineers compete to see who can get a soap box down hill in the fastest time.
Guy Martin has even taken on the challenge to see just how fast a soap box cart can go.