When I saw pictures of this a couple of years ago it went straight onto my 'must see' list and considering it is in Duisburg, which is only half an hour away from my parents' house in Germany, it clearly was only a matter of time. Well, I was in Germany again last weekend and finally made it and it is AMAZING!! This walkable roller coaster is the work of artists Heike Mutter und Ulrich Genth and is built on a mount of rubble dug up by local coal mines (of which there were plenty in the area). Thankfully it was a miserable day so no-one was around and we had it almost entirely to ourselves!!