The small square fort Kotanaka was built in the 18th century by the Dutch East India Company. It stood next to the keraton (Palace) of the Sultan of Ternate. The fort served in the first place to keep an eye out on the kraton and remind him of the presence of the company.
It was also part of the series of small fortifications that protected the coast before the city of Ternate. The fort was to the stream that there sprang also called "Santosa".
Fort Kotanaka is owned by the family of the sultan. The fort is built of natural and brick with as adhesive a mixture of lime and sand. At the recent renovation, the original steps and walls were covered with imitation-stone reliefs made of cement.