Fort Buitensluis lies south of the village of Numansdorp, in the province of South Holland in the Netherlands.
Fort Buitensluis was built as a solely earthen fort in 1793. It was named Fort Buitensluis after the old name for Numansdorp. It was strategically situated at the mouth of the harbour of Numansdorp, on the north bank of the Hollands Diep water, opposite the fortified town of Willemstad.
In 1862 the fort was strengthened and several bomb free stone buildings were erected; powder magazines and barracks. In 1874 it was incorporated into the 'Position at the Hollands Diep and Volkerak' together with Fort Sabina, Fort Prins Frederik and Fort Hell.
In 1915 Fort Buitensluis was mobilized and again strengthened. This time with the use of reinforced concrete for cannon positions and bunkers. At the beginning of WW II it was armed with 21 cannons. Although it is said these cannons dated from 1887. During WW II the fort was used by the German army. After the war it was used as a prison camp for collaborators and former members of the National Socialist Movement until 1949.
The fort stayed in military possession until 2013. It was used for military exercises and a caravan park for military personnel.
At present there is still a small caravan park inside the fort. Fort Buitensluis can be visited for free but only on a couple of days each year. Hopefully it will be opened more often in the future. A nice fort.