Balle perdue (Lost Ball) is a happening achieved by two artists, Dector and Dupuy, in 2014. It consists in a guided tour of the fifteen kilometers between Caen and the English Channel. Through the concept of work of art-place, theorized by Anne Volvey, this paper analyzes this art work’s effects on the viewer’s spatial perception and the ways it creates some territory, cross-examining in return the complexity of this notion on a geographical point of view.