Open Streetmap is a map service which lets you use a very high-standard map based on open source software.
The web service is available to create maps for use on a website, and you can create maps using OSM data for walking trips with You can even host your own OSM server - see more on Swith2OSM.
The OSM data are crowdsourced, so it is very possible to contribute with data on areas you know - you can even complete missing data using the app StreetComplete.