Does the ride have to be a "thing" like the C2C or whatever. There's lots of lovely and varied countryside around the midlands, indeed all over the country. You could pick a couple of intermediate destinations, pretty much anywhere (avoiding conurbations and hideously hilly bits). It could be thoroughly unremarkable but the real ingredient will be you, riding along with your friends, having fun.
Or go and ride around in France. The thrill of getting the ferry with your bikes (OK, I'm easily thrilled) and then a succession of pretty Normandy towns in which you can scoff huge quantities of patisserie.