The Holy Cross Church stands at the top of the old town, and its Baroque interior is one of the most lavish in the region — extravagant even by the high standards of south German ecclesiastical decoration. It was built between 1717 and 1720 by the Vorarlberg school, a network of builders and craftsmen from western Austria who spread the south German Baroque style across the region in the early eighteenth century. The stucco work is elaborate, the frescoes expansive, and the whole interior has a theatrical confidence that reflects the building's significance.
The church's importance predates the Baroque fabric by several centuries. It was built to house a relic of the True Cross that had been venerated in Donauwörth since the medieval period, and it was around this relic — and the disputes over Catholic processions connected to it — that the notorious Donauwörth Incident of 1606 unfolded. The incident, in which Protestant townspeople disrupted a Catholic procession, led Emperor Rudolf II to place the town under imperial ban and allow the Duke of Bavaria to re-Catholicise it by force. Historians regard this episode as one of the flashpoints that helped set central Europe on the road to the Thirty Years' War.
The relic is still housed here and still venerated. Visiting outside of service times is straightforward; the church is rarely crowded.