This former Dominican convent (1232), the chief seat of Rhenish mysticism in the 14th and 15th centuries, became a museum around 1850, and it’s been a treasure house of the art and history of Alsace ever since. An ambitious project to double the exhibition space to show off its modern and contemporary art collection includes the neighboring former municipal baths, an Art Nouveau building, and a new structure designed by Swiss architects Herzog and de Meuron.

The jewel of its collection is the Issenheim Altarpiece (Le Retable d’Issenheim), created by Würzburg-born Matthias Grünewald, “the most furious of realists,” around 1515. His colors glow, and his fantasy will overwhelm you. One of the most exciting works in German art, it’s an immense altar screen with two-sided folding wing pieces—designed to show the Crucifixion, then the Incarnation, framed by the Annunciation and the Resurrection. The carved altar screen depicts St. Anthony visiting the hermit St. Paul; it also shows the Temptation of St. Anthony, the most beguiling part of a work that contains some ghastly birds, weird monsters, and loathsome animals. The demon of the plague is depicted with a swollen belly and purple skin, his body blotched with boils; a diabolical grin appears on his horrible face.

Other attractions include the magnificent altarpiece (dating from 1470) of Jean d’Orlier by Martin Schongauer, a large collection of religious woodcarvings and stained glass from the 14th to the 18th centuries, and Gallo-Roman lapidary collections, including funeral slabs. The armory collection contains ancient arms from the Romanesque to the Renaissance, featuring halberds and crossbows.