The Ikebukuro Berserkers Colosseum, or simple the Ikebukuro Colosseum, is the headquarters for the Berserkers. It is located in Ikebukuro. Although originally known as Arti del Teatre, the interior has been repurposed for combat among battle seekers.
Structure
Its facilities are completely enclosed by the building. As such, it made a suitable location to test summoning an Exception in Chapter 3. It also restricts entry tightly, with the main entrance typically guarded by 
Garmr.