This is a particularly lovely riverside walk to Elter Water Lake and Skelwith Bridge from the village of Elterwater. There is a nice surfaced path running from the village to the lake along the Great Langdale Beck and the River Brathay. It's a popular walk with the tranquil river one of the most pleasant areas of Great Langdale. There is also something particularly peaceful about the lake which is many people's favourite. The walk includes a woodland section by the lake before a visit to the wonderful Skelwith Force Waterfall at Skelwith Bridge. The falls are not particulary high at around 16ft but they are a wonderful sight after a lot of rainfall. There is a good viewing platform where you can get very close up to the falls. Just after the falls you come to the excellent riverside cafe which is a perfect spot to refresh yourself before the return leg. It's a nice easy walk with splendid views of the surrounding fells including the Langdale Pikes.
There are more great Elterwater walks to try if you'd like to extend your exercise. You could visit the splendid Colwith Force Waterfall or climb to Loughrigg Fell and Loughrigg Tarn. From Loughrigg Fell there are splendid views over Rydal Water and Grasmere Lake.
If you head west from the village of Elterwater you can follow the Cumbria Way along the Great Langdale Beck to Dungeon Ghyll. Here you can climb alongside the waterfall on a series of stone steps to Stickle Tarn.