In case anyone is interested in 3D Terrain simulation (specifically for GPS tracks, e.g. hiking, skiing): I'm working on https://cubetrek.com
Source is here: https://github.com/r-follador/cubetrek
Source is here: https://github.com/r-follador/cubetrek
I think version 3 is now in beta and last I checked they even covered remote areas and alp huts: https://www.swisstopo.admin.ch/en/landscape-model-swissbuild...
For CubeTrek, however, I needed some kind of dataset with global coverage, that's why I settled in SRTM data.
What kind of format is it?
Edit: did you mean GPX files? Yes! And FIT files.