You can self-host or run locally Valhalla (https://github.com/valhalla/valhalla https://github.com/valhalla/valhalla), reading in data from OSM as a starting po

You can self-host or run locally Valhalla (https://github.com/valhalla/valhalla https://github.com/valhalla/valhalla), reading in data from OSM as a starting point. (For my purposes, I went with local running, generating walking-distance isochrones across pretty much well the entire UK)