Ulsan Metropolitan City holds a long tradition of implementing ecopolis development building upon the “Ecopolis Ulsan” declared back in 2004. As one of actionable strategies to reduce the oil refinery’ climate footprint, thereby contributing to the ambitious carbon reduction target of Ulsan, this chapter provides insights from a circular economy perspective on the efficient use of the industry waste. Based on learnings from the city’s green and sustainable transition, the chapter addresses the experiences in a selected industry along with innovation solutions to shape the future of Smart Ulsan Eco-Industrial City. This case study showcases an innovation project for public–private partnerships (PPP) for industrial symbiosis and cross-sectoral collaboration for decarbonizing industrial cities.