I did that once. We went with the train to Geneva and crossed there by foot the border to France. We walked along a route thats called ‘Camino de Santiago’ which leads from Belgium to Spain. We never knew how much we’d walk in a day, where to sleep next or where to get the next food. Sometimes it was hard to find a place to rest because camping in the wild is forbidden and there was no camping place around.
It was a very special experience. At the end of the week we walked about 400 kilometers and were nearly dead^^
But I have to say it was really worth the experience!!!