Thanks Lit.
I just figured out how to find it in English. Wiki homepage, English language. No entry, but it suggested:
In 1909, the term 'wandelvierdaagse' was introduced for the first time in the Netherlands. The Dutch Association for Physical Education (NBLO) organised in those days walking marches. During the Second World War these 'walking marches' where prohibited by the occupation forces.
Since there was in the area ‘het Gooi’ a large number of walkers who needed a walking event, the walks developed under the term wandelvierdaagse. These walks were first held in 1940 and this was soon followed in other places in the Netherlands. When the occupation forces found out from this new form of walking events, they were banned because they were seen as assembly against the occupiers.
After the Second World War, the wandelvierdaagse was by various municipalities and local associations re-established and shortly, plenty wandelvierdaagsen where held again. Currently it is even so well established that in almost all places in the Netherlands there are wandelvierdaagse and that sometimes they have grown into major events such as the Nijmegen Four Days.
Distances [edit]
Often wandelvierdaagse are offered in 2 or 3 distances, namely: 5 kilometres, 10 kilometres and 15 kilometres. It is usually not the case these distances are walked all the 4 days, but that the total distance in those 4 days represent the amount of kilometres. In many places, on the last day all participants walked the same distance.
Large walk events (such as the Nijmegen Four Days) are much greater distances walked, here it is then thought to distances of 30, 40 or 50 kilometres.