Fort bij Hoofddorp in Haarlemmermeer

You're standing at the Fort bij Hoofddorp, also known as Fort van Hoofddorp. It's part of the Defence Line of Amsterdam, a ring of forts around the capital that's on the UNESCO World Heritage list. Look at the water all around it. The fort sits on its own island, in a bend of an old military dyke and right next to the Hoofdvaart canal.