The children wanted to build towers outside yesterday. The problem with towers is that then they want to sit on them. The problem with sitting on towers is getting up onto them. That's when you have to solve problems by making steps. You have to take turns because it would be too dangerous to all try to climb at the the same time. You need to make alternative towers for the children who are waiting their turn. You need to be aware of wobbly and unstable bricks so that you can fix them before they topple.
This child instigitated activity was very unnerving for me as an adult, but for children they learned to solve problems, take turns, create stable structures, organise themselves, take risks and develop their language skills. It lasted for an extended period of time and was very self absorbing.