Different chests and boxes have been hidden on the race track. You'll accumulate them as you race! All of them are locked, though; the keys are kept here and will unlock your chests at the end of the comp.
Racing requirements and content of the chests :
At least 20 races = Soggy box (100k)
At least 50 races = Small case (500k)
At least 100 races = Elegant coffer (800k)
At least 140 races = Runic chest (1M)
Unknown requirement = Antique key (???)
Don't forget that the rewards are cumulative, so you can get all of them! Good luck
Descriptions :
Soggy box : A wooden box. Looks like racers splashed water on it with their cars; it's damaged in places and very muddy. Eeek is that a slug?!
Small case : A nice, cheap little box. It seems to be in pretty good condition. Can't wait to open it!
Elegant coffer : That's such a refined, sophisticated looking box. It's got a small, finely crafted lock and delicate, golden engraved lines seem to form artistic patterns on it. How beautiful...
Runic chest : Now that's an interesting one. It's made of dark wood, and engraved with indecipherable runes. With a start, you notice that those runes are in fact made of mirrors. The chest is very heavy and you can feel an intense vibration emanating from it, along with an irresistible desire of opening it...
Antique key : You find the key well hidden in a bush, and you have to extricate it from huge oak roots that had grown over it. It's big and really old for sure, with that dull silver color, as if the years had made it lose its shine. As soon as you pick it up, you begin to hear some kind of unintelligible whisper coming from the key. It's sort of creepy, so you drop the key, and the phenomenon stops instantly. Uuuh... let's leave that thing alone.
...
But you're fascinated with it, so you decide to take it to the comp host and grab the odd key anyway. What could it unlock?