On Easter Sunday 8th April, the annual Kiltwalk for children's charities takes place. It begins at the home of Scottish Football, Hampden Park and ends 26 miles down the road at Loch Lomond. For the less fit there is a 10km walk around the shores of Loch lomond on the same day
http://www.thekiltwalk.co.uk/main/training.html
A marathon length walk may be a bit much for me and its too late to train for it so I will probably take the easier 10km and more scenic route