How to find your way in difficult terrain, with obstacles, hazards, and deep snow? We present a solution for cross-country path planning and mobility, based on OSGeo software and open data. A large graph representing terrain, roads, and paths is stored in PostGIS for use with the pgRouting module of shortest path algorithms. The graph is based on detailed topography, soil type and vegetation data, and edge weights can be adapted for hikers and vehicles. The application is service oriented and held together by the Web Processing Service (WPS), the OGC interface standard for computation-oriented web services. A key component is the ZOO WPS server. The presentation will discuss WPS benefits and describe graph and weight generation, including challenges such as accounting for dynamic data about temporary hazards, weather, etc.