I spent a night at my friend's house on minecraft and built this epic pig race map! I'm wayyy too lazy to write down the whole description out again, so go take a look at the build on planet minecraft. Leave a diamond if you have an account!
Basically, there are two race tracks that are changeable through a set of commands in command towers. one is a basic figure-8, another is a "challenge path". They are both epic, try it out when you have friends over for a fun thing to do!