Wolf's Lair (Wilczy Szaniec in Polish, Wolfsschanze in German) was Hitler's main wartime military headquarters in eastern Prussia, used from 1941 to 1944. It is now a ruin open to visitors: a complex of massive concrete bunkers in the Mazurian forest, deliberately demolished by the retreating Germans in 1945 but so massively built that the explosions only cracked the walls. The effect — enormous slabs of reinforced concrete heaved aside and split, trees growing up through the floors — is more atmospheric than any deliberately preserved monument.
The site covers about two square kilometres and takes two to three hours to explore. The largest bunker, where Hitler lived and worked, had walls 8 metres thick. The briefing room where Stauffenberg's bomb exploded can be identified; placards in Polish and German explain the layout. There is a simple cafe on site and a small museum with maps and photographs. The site is near Kętrzyn, about 45 km north of Giżycko.