Pampus is an artificial island and late 19th-century sea fort located in the IJmeer near Amsterdam. Pampus now belongs to the municipality of Gooise Meren and is open to visitors.
Together with the artillery battery on the lighthouse island near Durgerdam and the battery at the Diemer seawall, Pampus protected the entrance to IJ Bay and the harbour of Amsterdam. Pampus was part of the Defence Line of Amsterdam. In 1996, UNESCO designated the entire Defence Line with its 42 forts a World Heritage Site.
Wikipedia https://en.wikipedia.org/wiki/Pampus
Coordinates 52°21'53.159" N 5°4'8.346" E