Without any doubt one of the best experiences in Berlin. Yeah, one of the best so far.
I slept in Teufelsberg, literally, Devil's Mountain, Berlin’s highest mountain (115 meters), created from the rubble of bombed-out Berlin after the Second World War.
At the top, there is a huge tower and two white domes of the former American radar facilities, with which NATO sought to listen in on East Germany. Its necessaray to climb a fence (there are some hole, though!), but it's really worth it.
It's a great place to take pictures. And along the night you'll feel different types of feeling and sensations: silent, loneliness, sound of the wind, or storm, fear, but above all, lots of peace.