Go to Colmar in the centre of Alsace (between Strasbourg and Mulhouse). Leave Colmar by the south and take N83 (and not on the motorway) towards Belfort. The Wettolsheim exit is indicated quite rapidly.
Once arrived in Wettolsheim, go to the centre of the village (church). When you get to the square (church, town hall), turn left on the rue du Château, go past the cave (an imitation of Lourdes) and take the first left. That is immediately on the right.