Sainte Waudru is the founder of the town of Mons.
On Saturday evening (at 8 pm) the shrine is taken down from the altar and given to the town authorities to keep during the festival.
It's a very moving ceremony and really worth to see.
Or watch this video if you can't make it.
Make sure you come to the church before 7 pm and don't forget to touch the shrine and the head reliquary of Sainte Waudru for good luck.