The advent of the Internet of Things (IoT) has led to the proliferation of sensor networks, enabling a new era of connectivity, data collection, and automation across various domains. IoT-based sensor networks comprise interconnected sensors and actuators that collect, transmit, and process data to provide valuable insights and enable intelligent decision-making. This paper explores the architecture, applications, and challenges of IoT-based sensor networks. The architecture section delves into the components, layers, and communication protocols that constitute these networks, highlighting the roles and interactions of sensors, microcontrollers, gateways, and cloud services. The applications section showcases the diverse use cases of IoT-based sensor networks in smart cities, industrial automation, healthcare, agriculture, and environmental monitoring, illustrating their transformative impact. The challenges section identifies the key issues such as scalability, interoperability, security, reliability, energy efficiency, and data management that need to be addressed to realize the full potential of IoT networks. Finally, the paper discusses future directions, emphasizing the potential of edge computing, 5G, artificial intelligence, and blockchain technology to advance IoT-based sensor networks and unlock new opportunities. Through continued research, innovation, and collaboration, IoT sensor networks are poised to drive significant advancements in technology and society, creating a more connected and intelligent world.