Rainbow Way Galaxy is the final main level of Super Mario 64: Star Revenge and Redone. Even though there are stages which take place in main level slots (Path to Second Overworld is course 15 and SMB 1-1 is course 14), they only contain one star (though in order to get to the final Bowser, you need all of them). This level is on the second floor of the Starenemy castle. Just go through the pipe outside of the last course and avoid all the Starenemy Amps on this level of the fort.