Pikachu no Natsuyasumi

ピカチュウのなつやすみ

Ash and his friends arrive at a Pokémon-only park. They set all their Pokémon loose and, after Ash tells Pikachu to watch over Togepi, they enter for a day of fun and relaxation. Unfortunately, it's not going to turn out the way they had hoped. (Source: Serebii)