Unitymedia has this map of their "Wifispots" which is a second wifi network their newest routers will automatically open, which is free to use for all of their customers. What's interesting is that this also maps where people subscribe to their service. I'd love to see someone who knows their stuff analyze this map (it only loads if you allow it access to your location fyi) https://www.unitymedia.de/privatkunden/internet/unitymedia-wifispot/wifispotfinder/
@noiob I don't think there is, unfortunately :c
@Thaminga turning it off will lead to them pushing a new firmware to your router that disables that feature. I've been thinking of flashing my old router to create a Freifunk node, too, maybe there's something like that where you live (https://en.wikipedia.org/wiki/Freifunk)