Why do we build more than we need? While open spaces are becoming more and more scarce, we continue to overlook the possibilities of what has already been built. With this publication RE-ST puts the needless growth of the existing patrimony on the agenda. Wanderspace is built and unbuilt space that we have produced together but underutilized on a daily basis. Space that is present everywhere and nowhere on different scales. Nobody knows how much it is exactly. Detecting, mapping and activating wanderspace is a tasks and opportunity for the architect. Do not spill in houses, but in designs to re-use what is there and only build if there is no other option.