The Campanian Ignimbrite caldera occupies the Campi Flegrei region and part of the city of Naples. The previous caldera boundary throughout the northern periphery of Naples was merely inferred due to the lack of outcrops of proximal deposits associated with the Campanian Ignimbrite. The exact location of this important structural feature within the city of Naples is fundamental for the reconstruction of the volcanic evolution and hazard implications. New exposures and subsurface constraints reveal thick welded and lithic-rich successions overlying several monogenetic volcanoes. These proximal deposits are associated with the Campanian Ignimbrite and allow a better localization of the caldera boundary well inside the city of Naples, 2 km south from the previous limit. The caldera rim in this sector partially coincides with a vent alignment that represents a structurally weak zone through which the caldera collapse occurred. The minor displacement (few tens of metres) of the top of the sedimentary succession, beneath the volcanic sequence near the caldera rim compared with 3 km displacement of the top of the sedimentary succession in the central part of the caldera suggests the presence of a complex geometry of the caldera floor, which shows a piecemeal-like structure characterized by deeper blocks at the centre and shallower blocks to the sides.