Location from pokemon-unova by
The site of the Unova Pokémon League — a purpose-built tournament arena city north of Opelucid, where Ash loses to Cameron in the Top 8.
Vertress is the Unova League's sanctioned venue. The colosseum seats tens of thousands; the pool and fire arenas double as specialized battle stages. During the Unova League arc, Vertress hosts all 128 qualifying trainers, including Ash, Trip, Stephan, Bianca, Cameron, and Virgil. The bracket is live-broadcast across the region. Ash loses his quarterfinal (Top 8) match to Cameron's mid-match-evolving Lucario here.
A modern stadium complex surrounded by trainer dormitories, press booths, and a fountain-lined main plaza. Large holographic bracket display at the central square. Banners of previous Unova champions fly from the battle colosseum.