Outdoor Activity: Make Your Own River
My son made up a game that he is really enjoying outside: make your own river. He dug meandering shallow trenches all through a large mulched area under a hemlock tree and then pours water to make the river flow. He has even built a bridge out of bricks.
His little sister even likes the game too, and is an eager participant in bringing water to dump. If we fill up a five gallon bucket and bring it over then they can use small cups to tote the water back and forth and not waste too much.
I love it when my kids get in the zone and occupy themselves with creative, independent play. This certainly fits the bill and would be easily transferable if you have a place where kids can dig.