You take 1 tub of little cars and a tube add a slope, like a little step and you have tunnel speeding.
I have no idea what the tube was used for but the boys grandad gave it to us and its fantastic nice and heavy so they don't have the urge to move it around a lot. You could look for one at the local newspaper, often they sell the end of the ream of paper for a couple of buck that would have a nice tube in it, a postal tube would probable work just fine, in fact you could have a couple gaffa taped together so the kids could race their cars. Failing that a bit of pvc pipe would work great too.
|so much fun
|dog getting in on action
|plane too big (interesting to watch him work that out)
|big brother getting in on fun