Walk along the coast for long enough and you will meet a block of concrete in the dunes. Usually nothing tells you what it is. This site is here so you can look it up: what kind of bunker, from when, and which position it belonged to.
The map is not limited to the German Atlantic Wall. It also carries the casemates the Dutch army built in 1939 and 1940, the group shelters of the New Dutch Water Line and the concrete of the Cold War IJssel Line. 3.171 objects in 157 municipalities in all.
The locations come from OpenStreetMap, the free world map where volunteers draw in bunkers. Photographs come from Wikimedia Commons and are linked to an object when they were taken within eighty metres of it. Province and municipality boundaries come from Statistics Netherlands.
Most objects have no known name, and far from every bunker has been mapped. Draw a bunker on OpenStreetMap and it will appear here at the next update. Photographs can be uploaded to Wikimedia Commons with the location attached.
Many of these sites are on private land, in military training areas or in dunes you may not leave the path in. Do not enter bunkers that are not open to the public: they hold water, the concrete is loose, and bats winter in them.