To unlock this course you must get at least 2 s ranks in the survival type of race. I found the survival ones to be easiest with the buggy and shotgun combo. I actually got an s rank first time and the achievement didn’t unlock but then I replayed it and got a b rank and it unlocked immediately. I’m not 100% sure if it glitched the first time or if you have to get specifically a b rank for this but you will need an s rank for the all s ranks on all courses achievement