A full study of the giant, complex outer planet systems is a central goal in space science. Exploring these systems can help us understand better our solar system as a whole. According to the Decadal Survey , a full exploration of planetary moon systems of Jupiter, Saturn and Uranus are top priorities for the next flagship class tour and orbiting mission. In particular, a comprehensive visit of the four large moons of Jupiter, known as the "Galilean moons", is important to search for liquid water and extraterrestrial life. In this NIAC Phase One study, we propose a new mission concept, named Magnetour, to facilitate the exploration of outer planet systems and address both power and propulsion challenges. Our approach would enable a single spacecraft to orbit and travel between multiple moons of an outer planet, with no propellant required. Our approach would enable a single spacecraft to orbit and travel between multiple moons of an outer planet, with no propellant nor onboard power source required. To achieve this free-lunch 'Grand Tour', we exploit the unexplored combination of magnetic and multi-body gravitational fields of planetary systems, with a unique focus on using a bare tether for power and propulsion.