Today, I've signed up for the Ranscombe Challenge. A trail run of a 3.8m lap, with an 8hr time timit, so you can basically run as far as you want.
Those running 7 laps classisfy as a Marathon, those running 8 get classed as an Ultra.
The thought of running 26.2 miles at the moment terrifies me as I've not yet passed that distance but the Ultra was the target for 2015. I've just brought it forward by about a year. Nothing like a challenge.
More information here.