Sigmaringen is located on the southern edge of the Swabian Alb, a plateau region in southern Baden-Württemberg. The Hohenzollern castle was built below the narrow Danube river valley in the modern Upper Danube Nature Park (German: Naturpark Obere Donau). The castle rises above the Danube on a towering chalk projection that is a spur of the white Jura Mountains formation. The hill is known simply as the Schlossberg or Castle Rock. The Schlossberg is about long and up to above the river. On this free-standing towering rock, the princely Hohenzollern castle is the largest of the Danube valley castles. The sheer cliffs and steep sides of the tower made it a natural site for a well protected medieval castle.