Robin Z.
Yelp
Located just outside the main touristy areas of La Petite France is this must-see attraction. If you like wine, history, architecture, the art of cooperage, or all of the above, you will enjoy visiting this underground urban wine cellar, home to one of the oldest wines in the world. It takes about 30 minutes with the excellent recorded audio tour (headsets were 3 Euros when we visited). In addition to its storied past, it is also a working cellar, used by some local vineyards to age current vintages, likely as a novelty but you must admit that is charming and all proceeds go to raise funds for their landlord, the local hospital above the cellar.
As others have noted, it is not the easiest place to find. Put "1 Pl. de l'Hôpital, 67000 Strasbourg, France" in your Google Maps app and switch to street view, which may help you find the exterior staircase (on the yellow building) that leads down to the entrance.