Iron Island (Japanese: こうてつじまSteel Island) is an island off the western coast of Sinnoh. It is only accessible via ship from Canalave City.
The cave on Iron Island was once a prosperous ore mine, but it was shut down after the ore reserves dried up. Since then, it has been kept open as a training area and habitat for wild Pokémon. Byron, Riley, and the members of the Canalave Gym come here to train, as did Roark in his childhood. Galactic Grunts are also found within the abandoned mine.
The main point of access to Iron Island is at its southwest corner, which has a dock for access by boat from Canalave City. One of the openings to the inside of the island is blocked by ledges, and thus its role is more like that of an exit. In front of the dock is two sets of stairs, separated by a landing on which a cabin apparently owned by Canalave Gym Leader Byron is located. The stairs lead to another cave opening, the only other way to enter the island.
The cave inside the island is brown in Diamond and Pearl, and black in Platinum. In all three games, the floor of the cave throughout the island is lined with oil drums and I-beams, with the former occasionally serving as obstacles which the player must navigate around in order to access certain parts of the cave sections.
When the player first enters, a pair of stairs facing left and right provide access to the first basement of the island. The left stair leads to a dead-end section, in which a single Camper can be battled. The right stair leads to a larger cave section with several Trainers, where a platform lift at the end can be used to gain access to the second basement of the cave. Once again, there are two sets of stairs facing left and right at the end of the platform lift; this time the right one leads to a dead-end section, where two Workers can be battled. The left stair leads to the largest single cave section of the island, where Riley will partner the player the first time the player enters it, participating in Tag Battles with his Lucario. Following this point, the remaining Trainers present in the cave are set up in a way such that tag battles against them with Riley as partner are possible, though strictly optional save for the battle with the two Galactic Grunts at the end of the section.
After the battle with the Galactic Grunts, Riley will cease his partnership with the player, and presents them with a Riolu Egg as a parting gift; if the player's party is full, he will remain until the player returns with an empty slot in their party. The departure of the two Galactic Grunts will also allow the player to access another platform lift that takes them down to the third basement. A cave opening in the wall leads to the exit section with another lift, which will take the player straight back to entrance level, where they can leave the inside of the island. In Pokémon Platinum, this section also contains the entrance to the Iron Ruins, where Registeel can be battled if the player has a fateful encounterRegigigas in their party.
When entering the western portion of B2F of Iron Island for the first time, the player encounters Riley. He offers to travel through the rest of the mine with the player. He is one of the Stat Trainers, specializing in the Attack stat. While he is with the player, all wild battles become Double Battles, and all Trainer battles that would otherwise be Double Battles become Multi Battles. After every battle, he will completely heal the player's party. He leaves the player once they have reached the elevator leading to the exit of the mine. Before he goes, he will give the player a RioluEgg, if the player has a space for it in their party; if not, he will wait until the player returns with a free slot.
After receiving a call for help from Barry, Ash and his friends sailed over to Iron Island in Steeling Peace of Mind!. There, they encountered Riley and his partner Lucario and also uncovered Team Galactic’s latest operation. The group discovered that Team Galactic were trying to activate the Iron Ruins present on the island. The resulting low frequency energy waves were wreaking havoc, and responsible for all of the Steel Pokémon including Barry's Empoleon and later Riley’s Lucario to go berserk.
In Saving the World from Ruins!, Team Galactic activated the Iron Ruins using the stolen Spear Key to scan Mt. Coronet for the location of the Spear Pillar. Ash and the group succeeded in stopping Team Galactic's operation, and Riley and Lucario successively contained detonating bombs placed by Team Galactic which were to destroy the island. However significant progress was made towards Team Galactic's goal, as Mars and her Galactic Grunts still escaped with the Spear Key and Cyrus learned with definitive evidence that the Spear Pillar was somewhere on Mt. Coronet.
Later, Professor Carolina arrived to investigate the connection between the Iron Ruins, which were only uncovered because of Team Galactic, and Spear Pillar. She enlisted Riley's assistance, hoping his local knowledge would be useful. She revealed that Iron Island and the Ruins are made of the same compound as Veilstone City's meteorites. Later, Ash and his friends left for Chocovine Town.
After Diamond had completed the five rounds, Riley gave him one last training mission, telling him to retrieve a Pokémon Egg he had placed at the deepest part of the island. When Diamond found the Steelix that he had fought against during the first round defeated, Riley decided to accompany him for the round. Suddenly, they were attacked by a pair of Roughnecks, who blinded Riley and his Lucario, disrupted their Aura sense with their Mothim's Air Slash, and took the Egg hostage. As such, Diamond took on the Roughnecks himself, revealing that he had secretly been training on a way to make Tru's Razor Leaf faster. He had figured out that the attack became faster the less leaves it used, so he had trained Tru to launch only one Razor Leaf per attack, which made the move so fast it could strike before Diamond could even finish saying its name. With this technique, Diamond was able to defeat the Roughnecks' Vespiquen and Mothim, saving the Egg and allowing Riley to finish the Roughnecks off himself. Afterwards, the Egg hatched into a Riolu and Diamond headed back to Canalave City.