Complex sentence: The architects envisioned the high-speed train station as a permeable structure, which would have to serve as a mediator between the different spirits of the city, a new social hub and not only another piece of infrastructure.
Split into simpler sentences: The architects envisioned the high-speed train station as a permeable structure. The structure has to serve as a mediator between the different spirits of the city, a new social hub and not only as another piece of infrastructure.