From carriages to cars, from steam engine trains to HS trains, the modes of mobility has been changing through the time. Mobility as become more and more relevant to people’s daily life and also plays an important role in city planning. With the rapid development of mobility modes, more facilities are also needed to fulfill a complete transportation network. Nowadays, more and more infrastructures such as highways, railways, are built to connect different districts. These infrastructures are usually built elevated from the ground and create a large amount of leftover spaces underneath. Various problems such as lowquality space, divisions in urban planning, and safety issues will arise because of these leftover spaces. Therefore, my research question becomes: How to activate the leftover spaces caused by infrastructures in public places? From the researches, to activate leftover space, four aspects need to be paid extra attention to. The primary aspect is accessibility, which is the capability and opportunity of leftover spaces to be reached and entered. The second aspect is diversity, the fact of many different types of atmosphere, activities, people can be included into the leftover space. This aspect could attract users to these spaces while allowing them to stay. Thirdly, inclusivity, which is the capability of including people from all groups, especially vulnerable groups such as children, elderly people, and disabled people, and treat them all fairly and equally. By improving inclusivity, it could allow leftover space to be used by people from different groups. The final aspect is reconnection, which is to link the leftover spaces together and reconnect with the city and become part of the urban planning. In this study, Tarwewijk district in Rotterdam South was selected as the site for designing a new mobility hub to solve the leftover space problem at site, while targeting to increase the four elements of leftover space from the research outcome.By comparing the research and design, this thesis can provide a new perspective for rethinking the characteristics of leftover space and provide could further a new methodology for activating the leftover spaces in other districts as well.