Wilhelmstein is an artificial island with an area of 12,500 square metres (3.1 acres) 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. Since then the island hosts the Wilhelmstein fortress (German: Festung Wilhelmstein). 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.

• In 1772 the island was the base of the first German submarine, the Steinhude Pike.

• Official web site

52°27′37″N 9°18′28″E / 52.4603°N 9.3078°E / 52.4603; 9.3078