The Shimmering Island (輝く島, Kagayaku-shima?) is an island located by Esto Gaza on the Lost Continent in Final Fantasy IX. Located to the south of the Lost Continent, the Shimmering Island appears only at first to be a collection of glaciers.
Shimmering Island is a gateway between the world of Gaia and the world of Terra. It is unknown whether it formed on its own as a side-effect to the failed Fusion attempt, or if Garland created it. According to the Final Fantasy IX Ultimania Shimmering Island began glowing 1800 years before the game's start marking its opening as the portal between the two worlds.
This was also the time the world's calendar began. The light of the Shimmering Island is the radiance of the crystals emanating from the dimensional interval where Gaia and Terra are joined together, and is the subject of religious faith for the inhabitants of Esto Gaza. When the gate to Terra is open, the radiance is at its greatest.
Towards the end of disc 3, the party obtains four elemental mirrors from Ipsen's Castle. Traveling all across Gaia, the Hilda Garde III drops off two party members at each elemental shrine, where the Chaos Guardians make their abode. All four are effectively living seals to the entrance to Terra, and after all are destroyed, the Shimmering Island reveals a glowing, multicolored portal. The player may access the portal via the Hilda Garde III.
After Kuja destroys Terra, the gateway nested on the Shimmering Island closes, and it regains its former icy appearance.