Wolf’s Lair was the most important of Hitler’s headquarters, hidden in Masuria, a region of Northern Poland famous for its 2.000 lakes. It was the perfect place to set up an inaccessible complex of bunkers with lakes and swamps blocking its access. The complex, which would become one of several Führer Headquarters located in various parts of occupied Europe, was built for Operation Barbarossa's start – the invasion of the Soviet Union – in 1941. The top-secret, high-security site was in the Masurian woods about 8 km from the small East Prussian town of Rastenburg (now Kętrzyn in Poland). Three security zones surrounded the central complex where Führer’s bunker was located. Despite the security, an assassination attempt against Hitler was made at Wolf’s Lair on 20 July 1944. On the 25th of January 1945, due to the Red Army's rapid advance, the complex was blown up and abandoned.