The advent of Internet-of-Things (IoT) applications, such as environmental monitoring, smart cities, and home automation, has taken the IoT concept from hype to reality at a massive scale. However, more mission-critical application areas such as energy, security and health care do not only demand low-power connectivity, but also highly reliable and guaranteed performance. While fulfilling these requirements under controlled conditions such as urban and indoor environments is relatively trivial, tackling the same obstacles in a more challenging and dynamic setting is significantly more complicated. In environments where infrastructure is sparse, such as rural or remote areas, specialized infrastructure-less ad-hoc solutions are needed, which provide long-range multi-hop connectivity to remote sensors and actuators. In this paper we propose a new general-purpose IoT platform based on a combination of Low-power Wireless Personal Area Network (LoWPAN) and multi-hop Wireless Sensor Network (WSN) technology. It supports reliable and guaranteed real-time data dissemination and analysis, as well as actuator control, in dynamic and challenging infrastructure-less environments. In this paper, we present the IoT platform architecture and an initial hard- and software prototype. Moreover, a use case based on real-time monitoring and training adaptation for cyclists is presented. Based on this case study, evaluation results are presented that show the ability of the proposed platform to operate under challenging and dynamic conditions.