The Arena is a huge building, built in circle. It seems entirely made of stones, in order to look like a Coliseum. Inside, there is two receptionists: a Nidorina Gijinka and a Nidorino Gijinka. They are there in order to get your a spectator seat or to register you inside a tournament.
The upper floors all lead to spectator seats. The lower floors leads to multiple different rooms. Some of them are waiting rooms, some others are training rooms. All the waiting rooms lead to the main part of the Arena, the center where all the main battles happen. Scientists have built a system where the floor of this battleground can change.
Next to the Arena, there is a space almost as big as the Coliseum. It's a plain with the grass removed, and was intended to be the temporary Arena until the building was finished. It has been left as it was.