Particles coming from the universe are crossing the earth all the time – they are harmless but invisible to us. Cloud Chambers are detectors which make the tracks of the particles visible. Some decades ago these detectors were used at CERN in the first particle physics experiments. The following instructions will help you to build your own Cloud Chamber at home. You will also find explanations on what you can see in the chamber and what the source for this particles is. In addition, we link to similar resources, give advice on radioactive sources (e.g. radioactive balloons) and give an overview over solar, primary and secondary cosmic particles.