Indigo Plateau

Indigo Plateau is where you can battle the Elite Four and Champion Gary. You must have 8 badges to enter Victory Road which then leads to Indigo Plateau.

There is also an NPC to teleport you to Elegant Valley where you can EV and IV train your pokemon.

Talk to one of the two guards inside the hut in Indigo Plateau to battle the Elite Four which then moves on to Champion Gary.

There are also many NPC's that either give you advice or bring them certain pokemon for something in exchange (Giratina-O and Regigigas).

A PokeMart and a PokéCenter are also located inside of the facility, but are unavailable during your Elite Four challenge until you defeat all members or are defeated yourself.