When Nazi Germany invaded Poland in 1939 significant strategic emphasis was placed on the capture of the Bydgoszcz bridgehead, a series of fortifications which safeguarded Poland’s western flank. Defended by the 15th Wielkopolska Infantry Division the network of trenches and bunkers came under sustained attack on September 3, 1939, and after a day of fierce fighting the Poles were forced to retreat towards Bydgoszcz in the face of overwhelming odds. Today the ten kilometre trail of bunkers make for an interesting day out, and includes an open air museum consisting of reconstructed trenches and observation posts. Officially opened by surviving veterans on September 15th, 2005, the trail begins at the town of Zielonczyn – a thirty minute train ride from Bydgoszcz – and concludes at the town of Osowiec. There’s 17 bunkers in total, all of them in differing states of disrepair, as well as five information boards detailing the story of the siege. The bad news, however, is they’re a real bugger to find - arm up on info before you leave at Tourist Information. Do also note that the route is tough work on a sunny day, and bring sturdy boots, plenty of water and a fearless attitude to fighting through brambles.