When I lived in NorCal, there were always lots of riders available to do centuries, double centuries or something in between (an overnighter to the coast, a favorite of ours, was 270 miles), so I rode a lot of disorganized group centuries and such. Here in Oregon, there just aren't many people who ride any distances and the local riding skill level is a bit below my safety threshold, so I ride a lot of centuries and double centuries solo or with my wife on a tandem.

While I enjoy riding with other people, my favorite rides are unsupported centuries and doubles on a tandem with my wife. If one of us wants to stop for a while, we don't have to justify it to anyone. If we want to go hammer and tongs for a few hours, we just do it. When we find an interesting looking old right-of-way like Gunter-Alma Rd, we head off on it. When it turns to gravel and then single-track, we just keep on enjoying ourselves and no one talks us out of seeing where it comes out. Of course we are totally on our own if something goes wrong, but we're not afraid of walking a bit, if need be. (We do have a Spot set up to notify a few friends where we are and if we need help, but we've always managed to make it home under our own power.)