With the explosive growth of smart city and Internet of Things (IoT) applications in recent years, a series of efforts has been undertaken to bring more intelligence to the smart cities and public transportation to solve essential problems like human surveillance for safety, traffic, and congestion management. In this article, we define a fifth-generation (5G)-envisioned architecture to enable cooperative sensing in the IoT for smart beaches and intelligent transportation systems and to develop a reference end-to-end implementation exploiting big data. Currently, many beaches are able to offer urban sophistication, but they lack a safety and connectivity infrastructure. Similarly, the dependence on road transport in our daily lives has grown massively, along with the problems arising from its use: permanent congestion, energy waste, and excessive carbon dioxide (CO2) emissions. We aim to address these safety and connectivity challenges and thus make a qualitative leap toward the future IoT and big-data application for smart cities and mobility. We present an architecture that raises the implementation of a platform to merge and integrate heterogeneous data sources into a common system and provide a set of advanced tools for the monitoring, simulation, and prediction to achieve a safer, less congested, and better connected beach. Our results will enable advanced surveillance at beaches along with traffic and travel management strategies based on reliable, real-time input data. The effectiveness of such new strategies, together with the proposed system, is assessed in field trials.