Today's publicly available pedestrian navigation systems still use paradigms developed for car navigation. In this paper, we present a novel landmark-based pedestrian navigation model using open source tools and open data from OpenStreetMap, which is available globally and free of charge. This approach ensures that our landmark navigation model is widely applicable, rather than restricted to a certain area with exceptional data sources. Our contributions cover algorithms for extraction, weighing, and selection of landmarks based on their suitability, as well as the generation of landmark-based navigation instructions for a given pedestrian route. The system has been implemented using PostGIS as a data store and QGIS for algorithm development. First field tests with pedestrians show promising results by confirming that our weighted landmark selection outperforms a simple baseline approach by reducing the number of navigation errors and revealed future challenges for the generation of intuitive pedestrian navigation instructions.