I've just come across welcometomygarden.org a Belgium based (and focused) website intended for people traveling under their own steam, like hikers and cyclists.

Sounds like a really nice idea to me. The website is very new - with both the concept and website whipped up during the Covid lockdown. The FAQ states the site's scope is limited to Belgium but the idea seems to have really taken off and their map shows sites now popping up in the Netherlands, France, Germany and England as well.