Radiant Emerald is the unlockable fifth stage in Sonic R. It is the only course which has to be unlocked, accomplished once you place 1st in all of the races on the Grand Prix mode. It is a magical rainbow course surrounded by crystals that swirls around planets through outer space! The ring gates here contain massive shortcuts, so use them to your advantage. Of all the courses in the game, this is easily the longest and most straightforward of the lot, and even if you open the shortcuts, completing one lap will still take a while. It is the only track to contain no Chaos Emeralds or Sonic Tokens.
By default, this course's theme is Diamond in the Sky. However, if you are to play as Super Sonic here, Super Sonic Racing will play instead.
- This level has major differences across different versions of the game - there is strangely a lack of transparency effects in the PC port whereas there were in the Saturn original. This is noteworthy since the true transparency effect was not believed to be possible on Sega Saturn since it was rare to see it happen on the hardware. In the PC port, Radiant Emerald was instead made solid and textures made use of flashier lighting. This also applies to the Sonic Gems Collection port due to being based off the PC version.
- This is the only course that cannot have any weather.
- This course is similar to the famous Rainbow Road courses from the Mario Kart series.
- Due to its nature as a secret course, no overhead map or manual description exists for this level.