Ardagger, Lower Austria, market town in the district of Amstetten, alt. 250 m, pop. 3,123, area 47.28 km2, comprises the towns of Ardagger Markt and Ardagger Stift, north of Amstetten at the entrance to the Strudengau valley. - Pumping plant of the Oesterreichische Donaukraftwerke AG (Austrian Danube power plant operator). - Gothic-Baroque parish church of St. Nicholas in Ardagger Markt. - Ardagger Stift: The collegiate monastery (founded in 1049) with its 17th-century buildings was closed in 1784 and transformed into a palace in 1813. Earlier collegiate church of St. Margaret, late Romanesque basilica (consecrated 1063, altered in the 2nd quarter of the 13th century) with raised choir and crypt beneath; Baroque stucco interior (1678). St. Margaret's window (1230-1240) is the oldest figural stained-glass work in Austria. The municipality is also home to a "Wehrmachtsmuseum" (military museum) with World War II weapons and the like.