At the 1970 World Expo in Osaka, master planner Kenzo Tange declared that the exhibition site could become the starting point for the development of a new city. This ambition, representative of the utopian ideologies of the architects of the period, prompts us to reflect on the reuse of the many infrastructures built during such events. In the run-up to the 2025 World Expo, which will be held on the artificial island of Yumeshima in Osaka Bay, the question of reuse arises. After six months of festivities, the various pavilions and the Grand Roof, a gigantic circular wooden structure 700 meters in diameter built for the occasion, will be completely dismantled. In a few years, in place of the exhibition, a tourist center will be built, housing Japan's first casino. Inspired by the ambitions of Kenzo Tange, my master project aims to propose an alternative solution which take advantage of the installations to create a sustainable complex including housing, public infrastructure and food production for a community of 2,000 residents, as well as a cultural center open to all. The grand roof structure, Symbol of the Expo 2025 will serve as the basis for the creation of this Circle City.