The Bourtange fortress is also referred to as the fortress that was never conquered. The order for the construction of an initial reinforcement to an important passage through the marsh was given in 1580 by the illustrious William of Orange. The fortress was at its largest in 1742. The information centre (the fortress entrance building) is the basis for a visit to the fortress. In addition to a concise visual introduction about the history of the fortress, they provide information about contemporary Bourtange. The Bourtange fortress is open all year, and the restaurants and shops determine their own individual opening hours. An entrance fee is charged for a visit to the Bourtange fortress museums; combined admission tickets are available in the information centre.