JUST because we don't have a stream in our back garden doesn't mean we can't make one with a hose pipe. This works particularly well if you run the water over an area of bare earth, and clay makes such lovely red mud! Just the thing if you want to hide or swing through the trees like Jane of the Jungle.
(Come to think of it, these are the knickers that Emma always puts in Alexander's drawer. She says she knows it's 'clean dirt' but she doesn't like them now they're not white any more.)