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Korea Demilitarized Zone (DMZ), Korean Peninsula
The first nature reserve on our list wasn't even supposed to be one — the Korean Demilitarized Zone (or DMZ) is a strip of land 2.4 miles wide and 155 miles long that divides Democratic People's Republic of Korea (North Korea) and the Republic of Korea (South Korea), and was formed in 1953 to provide a buffer zone between the two warring nations. Untouched by humans since, the zone has become a lush and densely forested de facto wildlife sanctuary. It is now home to rare species like the Asiatic black bear, leopard, Eurasian lynx and even the very rare Amur tiger.
But while it may be a sanctuary for wildlife, it is terribly dangerous for humans — the zone is littered with land mines and tank traps, and anybody attempting to enter it is liable to be shot by patrolling guards.