Wilhelmstein is an artificial island with an area of in lake Steinhuder Meer, located in the Hanover Region, Northern Germany. The island was created in the 18th century as a fortification by Count William of Schaumburg-Lippe, ruler of this small German state. The man-made isle (Count Wilhelm of Schaumburg-Lippe had the island built between 1761 and 1765 for his military fortress) hosts the Wilhelmsen fortress (). Today the island, close to Hagenburg, is a popular destination for tourists. It can be reached by so-called 'emigrants boats' from Steinhude and Mardorf.