When I lived in Gothenburg I had some friends who used to throw these outdoor parties in the summertime. They would choose a place; usually in a park close to their apartment and then the would bring a diesel generator and a sound system. They would sell beer (although the beer would always run out a third into the night) but never take entrance. Sometimes only their closest friends would show up and sometimes all of Gothenburg’s techno fashionista militia. There were never any trouble. The police never shut them down. Mostly because they never made any sort of advertisements or announcements. And the place was always secret and never spred in any organised way. The called it Minimal effort. Good times.