In European cities, 99% of virgin plastics are produced using oil and natural gas as raw materials, and fossil fuels are also used to generate the heat needed during the production process. This results in the emission of about 1.2 t of CO2 into the atmosphere for every t of plastic, considering just the production phase. If CO2 emissions related to the extraction and refining of fossil fuels are also examined, the production of 1 t of plastic results in a total of about 1.7 t of direct CO2 emissions. The EU cities use about 50 million tons of plastics per year, and it is projected that European Plastics’ demand will continue to grow to enable the resource-efficient products needed by society. In response to that issue, the global Plastic Smart Cities movement engages all cities committed to achieving zero plastic losses to nature. Since 2018, the initiative has supported cities and coastal towns in taking bold actions to stop plastic pollution, with the goal of reducing plastic leakage by 30% in the short term and achieving zero plastic in nature by 2030. Future research in challenges to plastics circularity is required in three main areas: Circularity by design, recycling, and alternative feedstock. Designing mindful plastic products and using plastics waste as a resource at the end of products’ useful life are crucial elements in a circular economy. Plastics are classified according to an identification system developed by the Society of the Plastics Industry (SPI) and taken up at the European level in Commission Decision 97/129/EC. The classification involves coding the most common polymers with numbering from 1 to 6, while the number 7 refers generically to all other types of plastics, which are not recyclable. In the face of the issues related to the accumulation and difficult disposal of different types of nonrecyclable plastics, the paper describes the experimentation design experience coordinated by the authors concerning the application of Circular Design Strategies for the design of different types of modular components to be used both in outdoor environments and for exhibitions, through the upcycling of one or more objects (rigid plastic containers for food use or high packaging) with Recycling Code 3 and 7. The methodology used is based on the recognized principles of Circular Design Thinking, aimed at identifying new opportunities for circularity and creating innovative sustainable outcomes, in line with the ONU SDG goals of Agenda 2030. It thus highlights the key role of Design, widely reiterated by European strategies related to the European Green Deal, through innovative and sustainable strategies which are human/environment-centered.