Mandatory Credit: Photo by Robin Utrecht/Shutterstock (11894470bw) Participants of the Mud Masters Fieldlab 2021 in action per day 5000 participants may come, all of the previously tested for corona. Because this edition of Mud Masters is a Fieldlab event, it is mandatory to have a corona rapid test taken. 5000 participants run over a muddy course full of obstacles. Mud Masters, Haarlemmermeer, Netherlands - 08 May 2021