The Ostrong is a ridge roughly 13 kilometres long in the south-western Waldviertel in Lower Austria. It lies north of the Danube, opposite Ybbs, and extends from the Danube to the Yspertal and Weitental. The Yspertal separates it from the Weinsberger Wald.
Geologically, the Ostrong belongs to the Bohemian Massif. It consists predominantly of paragneiss of the so-called “Monotonous Series”; on the southern slope the “Variegated Series” of the Drosendorf Unit comes to the surface. In the Miocene the primeval Danube flowed along its western and northern sides – through today’s Yspertal and Weitenbachtal.
Today hiking trails lead along the ridge, for example the Eisenwurzenweg (Austrian long-distance trail 08) from the Danube near Persenbeug to the Großer Peilstein. On trail no. 33 the view opens up over the Danube valley and the Alps.