The paper explores the emergence of territories that are constituted through spontaneous assembling of self-organized communities resulting in what we term urban social events. A concrete event is employed, namely Embros, an open occupation of an abandoned public building in the center of Athens, to highlight the dynamics that make urban social events transformative urban phenomena. By focusing upon the entangled mobilities of diverse agents, we explain how through differential, dis-continual assembling and creative collaborations, such urban social interactions institute unbounded and immanent modes of organizing. The paper contributes to organizational territoriality studies proposing that urban social events are mobile entanglements that institute practices of creative transactions with formal or informal communities. By doing that, it places the Arts, creativity and community participation at the center of transformative organizing.