Structural topologyStructuraltopology optimization is usually conducted within a predefined, fixed design domainDesigndomain. In this chapter, we demonstrate that the design domainDesigndomain can be flexibly redefined, serving as an effective driver for design innovation. By strategically exploring alternative design domains, we can generate a diverse array of geometrically distinct and structurally efficient designs, or create unusual behaviour such as mechanical non-reciprocityNon-reciprocity.