Calenberg, Mountain summit in Lower Saxony, Germany.

The Calenberg is a 70-metre-high hill of chalk marl in the Leine valley near Pattensen-Schulenburg, 13 km west of Hildesheim. Its southern part holds the ditches, ramparts and ruins of Calenberg Castle, a water castle begun in 1292; the northern slopes are farmed by the Calenberg Estate. The hill rises about 10 metres above the meadows and still stands out as an island during high water.

Calenberg Castle was built from 1292 by the Welf duke Otto the Strict as a lowland water castle on the southern part of the hill, in the Leine water meadows. Its moats had to be cut more than ten metres deep into the chalk marl. At the start of the 16th century the water castle was converted into a manor house and then a fort; after the Thirty Years War it lost its military role and was slighted. The ruins, with underground vaults and high ramparts, are now called Alt Calenberg.

The name Calenberg comes from Middle High German and Middle Low German kal, meaning bare or unwooded, because the chalk marl hill rose treeless from the Leine meadows. South of Alt Calenberg lies Lauenstadt, founded as a town in 1327 but never urban; in 1613 it ranked last among the Principality of Calenberg's towns. Until about 1900 open-stall markets selling everyday goods were held north of it.

The hill is bordered by the Leine to the north, Landesstraße 460 to the west and south, and gravel ponds to the east. The castle ruins and workers' cottages lie in the south, the estate farmland in the north. The moat was cut over ten metres deep into the chalk marl, and in high water the hill still stands out like an island.

The hill is a chalk marl slab formed almost 100 million years ago in the Cenomanian stage of the Upper Cretaceous, not during an ice age. A quarry north of the castle moat exposed four metres of this rock; Otto Seitz identified ammonites such as Mantelliceras mantelli and Schloenbachia varians there. The quarry was later used as a landfill and covered with topsoil.