Oostvoorne Castle, locally known as Burcht van Oostvoorne or Jacoba Burcht, lies in the village of Oostvoorne, in the province of South Holland in the Netherlands.
Oostvoorne Castle was founded in the 12th century. Who founded it isn't known although it's clear that they had chosen a strategic spot at the mouth of the Maas river.
First, a keep was built surrounded by a palisade and a moat. Although the keep stands on a motte of 10 meters high, its foundations rest on dune sand. The keep probably consisted of two floors above a vaulted cellar. Its walls were 2.60 meters thick. The keep had a thatched roof which, in the 14th century, would be replaced by wood and slates. The palisade was quickly replaced by brick ramparts.
During later repairs in the 13th century a gatehouse, a horseshoe-shaped bastion and a postern were added to the ramparts. Again in the 14th century a wall-walk, a square and two horseshoe-shaped bastions were added to the ramparts. The gate tower was reached over an arched bridge which led to a drawbridge.
Next to the motte a bailey was built to house the Lords of Voorne. The motte just served a defensive function then. The bailey consisted of a great hall, a chapel and several other service buildings like a bakery, a farm and stables. Outside the bailey lay an orchard and a vineyard.
The Lords of Voorne governed the province of Zeeland for the Count of Holland and resided in the castle till 1372. From then mostly landlords managed and resided in it.
From 1432 till 1436 Jacqueline, Countess of Hainaut (a.k.a. as Jacoba van Beieren in Dutch), was married to Frank van Borssele, Lord of Voorne. She lived in the castle for a only few weeks but her name stuck to it, hence the name Jacoba Castle.
After 1503 the castle became uninhabited causing it to decay. In 1534 the bailey with all its buildings was demolished.
In 1552 the keep and the bastions were demolished because they stuck out to much above the dunes which made them beacons for enemy ships.
In 1648 the castle ruins became property of the States of Holland.
Between 1724 and 1824 the ruins were private property. After which they became state property again. The Dutch State wanted to build a lighthouse on the remains of the walls on the motte so the walls of the castle ruin were all egalized and covered with soil. Eventually they built the lighthouse somewhere else. The remains of the castle were left covered.
Just another example of how historic remains were often treated in the Netherlands.
In 1934 the levelling of the motte started and restorations took place. The moat was also cleaned out. After WW II the foundations were built up again showing the plan of the castle. In 1958 further restorations took place.
In 1959, during construction works in the Hoflaan, workers found skeletons. It was the graveyard of the chapel in the bailey. From the bailey or its buildings nothing remains.
The remnants of Oostvoorne Castle can be visited for free, but you'll have to get the key to the gate at the local tourist information office.