The Defence Line of Amsterdam (Stelling van Amsterdam) is now decked out with stampion beacons. It is 135 km long defense line around Amsterdam and the beacons are placed around these forts. There will be about 20 in total to celebrate their World Heritage anniversary. The first one to collect all the stamps wins a prize. You can get hints for finding the beacons on Twitter, Facebook and Instagram.
Read more on iBeacon Nieuws.
Image found here.