Originally Posted by Judge Dredd
I never what you are talking about these days..lol is that the radar ? or an in game mission.
Depending on your version, there is a post game quest. I have W2, so I get White Tree Hollows in the White Forest. B2 and Black City has it's own version of this.
It's basically battle a lot of trainers with high leveled Pokes (haven't seen one trainer with anything under level 50) and have seen as high as level 68.
If you complete it, on W2, you get a shiny Dratini as a final reward. If you have B2, you get a shiny Gible as a final reward.
Throughout each portion of it (there are quite a few levels in it) you get smaller rewards, all of which seem to be stat boosting vitamins.