For an introduction to the great 15th-century heroine and the events that earned her fame – and shortly thereafter condemnation – don't miss this excellent site. It's less of a museum, and more of an immersive, theatre-like experience, where you walk through medieval corridors and watch (and hear via headphones, in seven languages) the dramatic retelling of Joan's visions, her victories, the trial that sealed her fate, and the mythologising that followed in the years after her death.
It's not coincidentally set inside one part of the archbishop's palace, where Joan was likely tried and condemned in 1431. A joint ticket with Panorama XXL is €15 for adults and €12 for children.