Wilhelmstein, Artificial island fortress in Wunstorf, Germany

Wilhelmstein is a fortress on an artificial island in Lake Steinhude, about 1.4 km from the shore. Built between 1765 and 1767, it has a star-shaped sconce with four bastions, a citadel and pincer-shaped tenailles. The outer walls are stone blocks, the interior brick; casemates housed soldiers and a small castle with a tower stands above them. The island measures roughly 100 m per side.

Count Wilhelm of Schaumburg-Lippe founded the fortress in 1761 as a response to the political tensions of his era. Five years of intensive construction were required to establish the foundation and build the defensive structures.

The island's name comes from Count Wilhelm of Schaumburg-Lippe, who had it built; the fortress still belongs to the House of Schaumburg-Lippe. The former commander's room now serves as a wedding venue, as it did around 1900, and since 2005 twenty couples a year may marry there. The museum displays maps, weapons and recreated living and detention cells.

Boats run regularly from Steinhude and Mardorf to reach the fortress across the lake. The island is open to visitors, but offers limited facilities, so it is helpful to plan ahead for food and supplies before making the crossing.

In its early years, the fortress served as a testing ground for military innovations and housed Germany's first submarine, the Steinhuder Hecht, built in 1772. A model of this pioneering underwater vessel remains on display at the island museum today.