High Quality Content by WIKIPEDIA articles! Calenberg Castle (German: Burg Calenberg, later called Schloss Calenberg and Feste Calenberg; ruins known as Alt Calenberg) was a medieval lowland castle in central Germany, near Schulenburg in the borough of Pattensen, 13 km west of the city of Hildesheim. It was built as a water castle in 1292 by the Welf duke, Otto the Strict, in der Leine river meadows between 2 branches of the Leine river on the southern part of the chalk marl hill of the Calenberg. At the start of the 16th century it was converted into a fort (Feste). In the 15th century, Fort Calenberg gave its name to the Welf Principality of Calenberg. Following the Thirty Years` War it lost its military importance and was slighted. Today it is a ruin with underground vaults that are surrounded by high ramparts.