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.

At that time the castellans (Burgmannen) in possession of the castle were the ministerialis family of Grubo or Grube, later Grubenhagen.

The castle gave its name to the Welf Principality of Grubenhagen founded in 1291 by Henry the Admirable.

In 1448 Henry III of Brunswick-Grubenhagen had to fortify himself in the castle, after he exposed himself to attack by Landgrave Louis I of Hesse following a raid in the area of Hofgeismar.

Instead the disappointed attackers devastated the villages of the neighbourhood: Altendorf, Reinsen, Bensen and Rotenkirchen.

As viceroy of the Kingdom of Hanover the duke had the timber-framed manor house in Rotenkirchen converted by master builder Laves into an elegant hunting lodge.

Grubenhagen Castle was neglected in the years after the Second World War and fell into further ruin.