Not all mountains are natural. Berlin’s Teufelsberg (literally “the Devil’s mountain”) is an artificial hill formed of millions of cubic metres of rubble that stands some 114 m high. It was built by the Nazis as a site for the Wehrtechnische Fakultät military training centre. At the end of the war, the Americans used it as their base for spying on the communications of East Germany. When the wall came down and the Cold War ended, the building and the giant ping-pong ball structures that crown this peculiar location in the Grunewald forest fell out of use and were abandoned. Nowadays, it serves as a viewpoint where graffiti artists from throughout the world come to leave their mark.