Participants in the International Four Day Marches Nijmegen, also known as the Vierdaagse, can expect to wind up with smelly socks and sore feet. Some 45,000 people take part in The Netherlands' largest -- and arguably most strenuous -- sporting event.Marchers spend up to 10 hours a day walking around Nijmegen, a municipality in the eastern Netherlands. The four-day event is a major festival. Over a million spectators line the route, cheering the participants on. Bert van der Land holds the record for having taken part in the most Four Day Marches -- he's already run it 63 times. He's especially looking forward to the third day, when the route goes along the Meuse River to Groesbeek's famous hills -- a real challenge for marchers.