From Bulbapedia, the community-driven Pokémon encyclopedia.
Way Away Island (Japanese: へオキノ島 Heokino Island) is a small, anime-exclusive island located off the coast of Johto, between Goldenrod City and Ecruteak City. It appeared in Carrying On!.
Map showing the location of Way Away Island
In the episode, Denjirō received a call from the Pokémon Center on the island. That Center's Nurse Joy told him that the needed medicine for the sick Pokémon had not yet arrived, even though Denjirō had sent a few Pidgey to deliver the medicine. Worried, Denjirō's grandson, Ash, Misty, and Brock decided to go and investigate the matter.
On their way, they found out that Team Rocket was stealing the Pidgey that Denjirō sent to deliver the medicine. They fought Team Rocket and managed to free the Pidgey. After that, they safely landed on Way Away Island and delivered the medicine to Nurse Joy.
Pokémon seen on Way Away Island