The Pokemon League is found within the Indigo Plateau just north of Route 23 in the Kanto Region. It is here were a trainer can battle the Elite Four and attempt to become the Champion of the entire region. In order to unlock the Elite Four, there are a few things you must achieve first. To start, you must obtain all eight Kanto Gym Badges. After this, you must head west of Viridian City on Route 22, and then north on Route 23 until you reach Victory Road. You must then journey through Victory Road, consisting of some of the best trainers found within the Kanto Region, until you make it to the Pokemon League. Only after you do all of this will you be able to battle the Elite Four.