DIY backyard obstacle course - actually worked out great
Built one with PVC pipes, old tires, and pool noodles last month. Cost me maybe $35 in materials I didn't have. The kids have been running it constantly. Pro tip: make it adjustable so different ages can do it without modifications. My 4yo can do the "toddler" version and my 9yo does the harder route. Keeps them both entertained which is basically impossible usually.
Pool noodles for obstacles - that's the hack I didn't know I needed. Mine was all PVC and wood and honestly kind of dangerous for the younger kids. Noodles soften it up perfectly.