Tough guy marathon

Joanna mentioned the Tough Guy marathon as one of the races that are a level more difficult than just walking 50km a day for four days in a row (in case you do not know it, I am referring to the Vierdaagse in Nijmegen). From the video on this website, I see her point. It is an extreme form of obstacle race, where you see the participants fighting to help themselves and eachother through mud, fire and ice cold water. Indeed if you complete this race you can call yourself a 'tough guy' and maybe even more so if you managed with no injuries...