At the centre of the world famous Rio Carnival is the Samba Parade ? a fierce competition of vast scale among 13 neighbourhood samba schools. Watching them are a panel of expert judges, more than 60,000 spectators and a TV audience of nearly half a billion. The unexpected is always expected during one of the largest parties on earth, and Nat Geo is right there to find out how Rio survives and Carnival continues to thrive.