The Cathedral of Notre Dame de Strasbourg follows the traditional layout of cathedrals. I think I have seen enough of these cathedrals to know that they follow a certain pattern. The central aisle and then the transept across it forms a cross shape. Usually around the altar area there is an area where people can move from one side of the church to the other without crossing the altar. Obviously, this is useful if there are services going on and you do not want to be distracting people by crossing right in front of the altar. This area behind the altar is the ambulatory. As the name suggests, it is a place to move.
The ambulatory in cathedrals and basilicas usually have small chapels around it. The Cathedral of Notre Dame de Strasbourg is the same. There would be places for people to pray and even give donations. While this practice has always been questionable to me, I also understand that the church needs actual money in order to operate. I was amused at one chapel which has a donation box but instead of a traditional box where you drop coins or money, this is probably the first one I have seen which accepts contactless. As traditional as the church may seems, it seems that slowly it has been starting to use modern technology beyond just the PA system.
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