Saint-Cyr Church is the main survivor of Issoudun's old religious landscape. The tourist office dates its origins to the early medieval period, though the building you see today is mostly later Gothic work with 19th-century completion.
Inside, look for the stained glass, the large painting above the portal, and the candelabra traditionally linked to Louis XIV. It is not a cathedral-scale stop, but paired with the White Tower and the hospice museum it gives the old centre its shape.