Radon is a radioactive noble gas formed in the Earth’s crust as part of the uranium decay chain. Over time, it seeps through layers of soil to the surface and can accumulate in higher concentrations indoors. Although radon is known primarily for its dangerous effects on human health, its short-lived decay products can be used to make simple radioactive samples for use in school lessons. This Master’s thesis presents the process of developing new learning activity based on the use of known radon experiments. The development of the activity took place iteratively in two stages. It is based on the theoretical framework of ISLE (Investigative science learning environment) approach and includes experiments with simple school laboratory equipment and radioactive samples resulting from the decay of radon.