Onstaborg was a borg (an old name for castle

Castle

A castle is a type of fortified structure built in Europe and the Middle East during the Middle Ages by European nobility. Scholars debate the scope of the word castle, but usually consider it to be the private fortified residence of a lord or noble...

 in some Nordic languages) in the village of Wetsinge, Groningen, Netherlands

Netherlands

The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

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The borg was built around 1500 by the family Onsta (also known as Onseda, Onsitha or Onsatha). The Onsta family belonged to one of the oldest and most prominent families of the Ommelanden

Ommelanden

The Ommelanden are the parts of Groningen province that surround Groningen city. Usually mentioned as synonym for the province in the expression Stad en Ommeland ....

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The Onsta family also owned an Onstaborg in Sauwerd

Sauwerd

Sauwerd is a village in the municipality of Winsum, Groningen, Netherlands.The village of Sauwerd is 10 to 15 kilometers away from its nearest city Groningen. The village is built on a wierde, to which it also owes its name. It is inhabited by an estimated 1,100 people...

. In 1658 the borg was sold and refurbished. In 1801 the borg was demolished. There is no trace left of the borg or its grounds.