From Bulbapedia, the community-driven Pokémon encyclopedia.
Lilly of the Vally Island (Japanese: スズラン島 Suzuran Island) is an anime-exclusive location in Sinnoh. The island is covered with mountains and forests. A town is situated on the southern end.
The island is the location of the annual Suzuran Conference and features amenities for competing Trainers just as other league locations do.