Wireless Sensor Networks (WSNs) have become one of the transformative technologies that support a variety of intelligent applications in smart cities, healthcare systems, and environmental monitoring programs. In this paper, a detailed survey of the recent developments in the design, deployment and optimization of WSN has been conducted in these key areas. It discusses the role of WSNs in sustainable urban infrastructure due to their capability to acquire data in real-time, intelligent transportation, air quality, waste management, and smart water. In healthcare, WSNs are used to remotely monitor patients, detect various diseases at their early onset, and implement improved emergency mechanisms, whereas in environmental monitoring, they facilitate the WSN enabling efficient evaluation of the pollution status, animal tracking, and catastrophe forecasting. Identified crucial issues in the study are energy efficiency, data security, interoperability, and latency, and the latest advancements in the field are mentioned, such as energy harvesting, integration of machine learning, and adaptive communication protocols. Future research aims at developing context-aware, scalable, and autonomous systems by integrating WSNs with the emerging paradigms, including Industry 5.0, IoT, UAVs, and edge intelligence.