In the 21st century, the role of railway stations began to change, as they began to integrate various modes of transport to become multimodal transit hubs (MTHs). They are often part of urban transformation plans due to the vast and underutilized spaces associated with them. This paper aims to reveal the changes in urban functions within transformed city areas due to the development of MTHs, as well as within MTHs themselves, by utilizing a widely accepted theoretical concept: the “15-minute city”. All conclusions are drawn by analyzing MTHs in urban transformation areas of European metropolises: Barcelona, Berlin, and London. The research shows that areas previously designated only for one use—industry—become areas with diverse urban functions after urban transformation. The reduction in infrastructural areas has resulted in the concentration of urban functions within these areas. This concentration can be observed in the following two ways: urban diversity has increased, and urban functions occupy significantly larger areas than before the urban transformation. It has been established that MTHs are catalysts for comprehensive urban transformation, as indicated by economic investments largely directed toward the development of urban functions in their surrounding areas.