Rainbow Road is the only location excluded from free driving in Mario Kart World’s Free Roam mode.
Free Roam lets players drive to locations across Mario Kart World's connected world, including areas away from regular race tracks and off-road sections. The mode is intended to make the game's environments feel like one explorable space rather than a menu of isolated circuits.
Rainbow Road is the sole stated exception to that freedom. Although it appears as a course in the game, players cannot freely drive to it in the same way they can reach the other locations in Free Roam.
This detail is easy to confuse with Mirror Mode, which horizontally inverts the entire map, or with Grand Prix, where racers drive between courses as part of a structured competition. The restriction applies specifically to Free Roam exploration.