Door of perception? In a way. This wall separates German and US compounds by not only nationality but also methods, principles, and ideals. The differences are stark in many ways. In an amusing show of gamesmanship, the Germans place a sign on the wall. As you entered the US side it said, in large letters, "DISTRICT 9" referring to the movie of the same name where space aliens are interned in a South African work camp. All in fun.