The Battle Castle has apparently stood for centuries, accumulating a massive, extensive library.
The Battle Castle is inherited by those in Caitlin's family. There is a hallway with portraits of past owners of the Battle Castle.
The Battle Castle is crowded and has long lines, but those lines move quickly.
You must win three sets of seven battles, 21 battles in all, in order to face Darach. Items are not allowed, but by winning battles you can accumulate "Castle Points" (CP) which function as currency, allowing the challenger to buy medicine, information on their opponents, and held items.
Seen Challengers' Pokémon