Wow, that sounds dangerous, a far safer option :doubt: would be Snowdon Mountain Railway and something like this, 2 skateboards and a bit of wood. But if you do it and break both your legs, just don't come running to me
https://www.youtube.com/watch?v=tRh2CC1ThQ8
Edit... if you did it at night and were prepared to run away from angry people... maybe could run like that all the way from Blaenau to Penrhyndeudraeth (give or take jumping off for a few level crossings, and maybe the new tunnel is flat?). I wonder with the right skateboards and speed on your side if you could do it in one go without walking?