The Mercado de Sao Sebastiao in Porto is a functional structure designed to optimize the flow of goods and pedestrians. Its architecture guides visitors through five levels connected by small steps, facilitating circulation and offering an overview of the space. The fountain at the entrance, the market’s only water source, serves as a gathering point and contributes to the site’s implantation into the urban fabric. The spatial organization follows a rational logic, with each vendor assigned a defined area composed of concrete modules, ensuring uniformity while structuring commercial activity. However, this approach limits possibilities for appropriation and flexibility. While the market effectively fulfills its role as a place of exchange, its layout shapes how users interact with the space. Today, in the absence of a suitable redevelopment, the city is considering its demolition, illustrating the challenges related to the evolution of urban commercial infrastructure.