The narrow road through the Masurian countryside winds alongside shimmering lakes and mossy swamps. It passes through sleepy villages filled with steep-roofed houses that, even on a warm summer’s day, look ready for deepest winter. This region of northeastern Poland is known for outdoor recreation. It’s a destination for hiking, horseback riding and other pursuits that thrive in clean air and boundless countryside. A peaceful escape. Suddenly, the road dives into a thick forest. Birds chirp high in the branches of deciduous trees. The scene is bucolic, but the setting is deceptive. An abandoned railway track appears first. Then, ruins...