The easiest way of making trails is along lines of opportunity: old railways, canals, flood-dykes and aqueducts. America 's National Park Service has been active in making long-distance trails, as has Britain 's Countryside Commission. Recreational trails can focus on particular categories of interest or they can be multi-purpose. The interest categories include history, scenery, ecology and recreation. London 's Silver Jubilee Walkway is a good example of an urban historic trail. It is a signposted walk through the city. Nature trails are found in urban and country parks. The Appalachian Trail , as proposed by Benton MacKaye in 1921, is the grandfather of recreational trails (Yahner et al 1995). It runs for 3300 km from Maine to Georgia in the eastern USA .