Walking

I have recently been doing lots of walking and I am loving it. I am trying to get out most days for at least an hour and then trying to do at least one longer walk each week too (currently the longest walk I have done is 11 miles). I would like to increase this longer one over the coming weeks as I am thinking of doing a walking event challenge, probably one organised by the Long Distance Walkers Association, which is likely to be 20 miles or more! Has anyone done one of these events and if so, would you recommend it?