When I lived in my home town as a kid, it had a charity bike ride every year and I rode in it a few times. I couldn't get anyone to sponsor me but I still went along for the ride which took you a couple of miles out of town into the countryside and then back into town to the sports ground from where it started. It was a good course that had some serious elevation changes but I was a little nervous because of the roads and traffic. My home town stopped organising it in recent years which is a great shame I think.
A couple years back there was an event on at Silverstone racing circuit, a 24 hour cycling event that I really wanted to take part in. It wasn't a riding constantly for 24 hours, more of a see how much distance you could cover in 24 hours. What my plan was was to get in an hours ride or so at the start, go to sleep until the early hours of the morning and then set off again until the finish. Sadly due to other things I couldn't take part and I don't think they will be doing another 24 hour cycling event at Silverstone any time soon.