Three dimensionality can be seen as architecture's fundamental existence, the profession's acclaimed domain. In times of globalism and scale enlargement, an update of this definition seems needed: metres turn into kilometres, 'M3' becomes 'KM3'. 'Km3' is a story about a world that is getting very dense. It constructs its logical response: a city that is denser. A city that is continuously under construction, with space for limitless capacities, populations and possibilities, a free-fall endless space.