Digital intelligence through information has contributed to the evolution of smart cities particularly in energy usage, human wellness, knowledge transfer, and urban development. Modern industrial, residential, transit, and commercial operations demand sustainable resource management and seamless communication. The sustainable environment has a network architecture to gather, store, and analyze the real-time data for effective decision-making. The Internet of Things (IoT) enables smart and sustainable environments by incorporating cutting-edge technologies to create smart, people-centric cities and industries. However, various security challenges and issues have raised from the ages of digital to smart cities. In this article, we present a systematic approach to depict the role of IoT in the ages. Various security challenges, real-time incidents, and countermeasures are discussed in this study to address the major difficulties of sustainable environments to highlight the potential visions of smart cities/industries