I have a 200k route where I am planning to ride back the next day. I didn't manage to design a second return route yet, it's somewhat remote and there aren't a lot of places to resupply. But riding the outbound route seems like it would be okay. I could also extend the same route to almost 300k, not sure about doing that. There is a route that the locals have been riding for decades that is 160km where they ride to a remote town, stay overnight, and then ride back.
It might be fun to ride something like that, but I did it because I'm trying to ride 10000km in brevets and permanents this year. Not sure I will ride it otherwise.