Grubenhagen Castle is a ruined medieval castle in North Germany dating to the 13th century. It is not far from the town of Einbeck in southern Lower Saxony.LocationThe ruins are located in the district of Northeim on a 298 metre high hill summit on the Ahlsburg ridge, south-southwest of Einbeck and east of the Solling hills, between the basin of the River Ilme and the valley of the Leine. The castle may be reached via a narrow forest path from Rotenkirchen, a village south of Einbeck, which is on the northern edge of the ridge and below the castle ruins and not far to the northeast.ArchitectureThe hill castle of Grubenhagen was built in the 13th century. Only the round, 18 metre high bergfried remains today. Attached to its southeastern side is a building from the 19th/20th century. The raised plateau of the inner ward, with its relatively small area, is oval and slightly kidney-shaped. It is about 63 metres long and 32 metres wide. Below it is the outer ward. The site is surrounded on three sides by a double ditch. On the fourth side the terrain drops away steeply, rendering a ditch unnecessary. To the northeast and southwest the remains of the ringwall and revetments have been preserved. A Merian engraving around 1650 shows the castle still with a round keep and a roofless building in front of it with a gable. On the outer ramparts of the main ditch was a defensive wall with a chemin de ronde behind the battlements to the northwest. To the north and northwest the engraving depicts the remains of another defensive walkway with embrasures.