First Day 1 Wii U purchase for me since Pikmin. BRING IT!

It's a mobius strip, thus it's an object with only 1 face... you drive round on the bit you can see in the image, then the half-twist corkscrew lets you drive underneath where you were before.

It's a concept that's been used a few times in futuristic racers. F-Zero GX has a great one that is more complex in that the track is transparent and also splits in the middle for part of the strip. (it's hard to explain, but if you understand the mobius strip bit, then look at the mario kart track in the OP and imagine you use a knife down the centre of the track from the metal section around till the corkscrew... You could also look up Casino palace double branches on YouTube, but it's probably hard to tell how it works without racing on it yourself)

Wow that's amazing!

My oh my, look at those wretched textures for the forest below the track. Totally flat.

Sorry, but there had to be something negative in here. You're lucky I went easy.

No, no. If there isn't negativity in Nintendo threads the balance of the universe will be thrown off.