Numerical simulations play an increasingly important role in modern science. In this work, we suggest using a numerical study of the famous perihelion motion of the planet Mercury (one of the prime observables supporting Einsteins General Relativity) as a test case to teach numerical simulations to high school students. The project was presented as a one day course at a student summer school. This work includes details about the development of the code (Python) for which no prior programming experience is needed, a discussion of the visualization as well as the course teaching experience. This course encourages students to develop an intuition for numerical simulations, motivates students to explore problems themselves and to critically analyze results.