Tir Nan Og é a capital das Fadas da Terra e foi bem um reino soberano em tempos antigos. Todas as fadas principais e outras Fadas Rainhas, como Diana - Rainha das Fadas Amazônica - e Aurora - Rainha das Fadas Árticas, da Terra recebendo ordens da Grande Fada Rainha de Tir Nan Og, exceto, até certo ponto, Sibylla que, como a fada da Justiça, tem de manter-se neutra e tratar amigos e inimigos, e as pessoas bem e mal como sendo todas iguais e não pode tomar partido. O fato de que até mesmo fadas de Tir Nan Og, sob ordens diretas de Morgana, não estão autorizadas a entrar em sua caverna quando ela deu abrigo aos Feiticeiros do Círculo Negro confirmando que o poder de Tir Nan Og tem limitações lá como é um lugar sagrado, mesmo que nebula, devido, em sua fome de vingança, mesmo proposta para atacar e destruir a Caverna de Sibylla para poder punir o Feiticeiros, já que Morgana era contra isso.De acordo com Morgana, Tir Nan Og era, antes da chegada de Ogron e seus Feiticeiros, um maravilhoso reino localizado entre a Dimensão Mágica e o mundo humano (agora na não magica, Terra), com magníficos edifícios e cenários e as fadas da Terra tinha contatos com todas as outras do reino mágico neste momento. Mais tarde, quando os Feiticeiros do Círculo Negro começaram a caça as fadas da Terra, eles usaram a própria ilha para aprisionar as fadas. Quando as Winx libertaram as fadas da Terra da prisão, ele foi usado como sede da campanha de vingança de curta duração contra os humanos.
O palácio real é onde mora a rainha das fadas. Nos corredores subterrâneos há as estátuas de todas as rainhas anteriores das fadas que já dominaram as fadas da Terra. O palácio em si parece a meio caminho entre um prédio e uma árvore, já que tem raízes gigantescas em sua base, e ramos com muitas folhas cor de rosa.
Existem Muitos menires na ilha.
Ele pode ser visto nos flashbacks a partir do último episódio da 4ª Temporada, que a última luta entre Morgana e os Feiticeiros do Círculo Negro aconteceu em Tir Nan Og, antes que Morgana foi selado em seu reino para o bem dos Feiticeiros.
In ancient times, Tir Nan Og was a magnificent place located between non-magical Earth and the Magic Dimension and the Fairies protected nature and spread its powers on Earth. Then the Wizards of the Black Circle developed a way of resisting to fairy magic and stealing their powers by plucking their wings. They started the Great Fairy Hunt and captured all the Earth Fairies, sealing them into their own kingdom of Tir Nan Og. As, one by one, all fairies of Earth were captured, the Wizards' power grew stronger and wars, intolerance, and all kinds of evil spread on Earth.
The Wizards tried to attack Bloom at Alfea, believing she was the last Fairy of Earth as she grew up in Gardenia, while she was in fact from Domino. Miss Faragonda then sent the Winx to Earth, with the mission of restoring magic on Earth and saving the last fairy of Earth, and the Earth Fairies as well. After the Winx gained the Believix powers, they began to make the humans believe in magic, weakening the Wizards and preparing Earth to welcome new Fairies, and they found the White Circle, the opposite of the Wizards' Black Circle.The island first appeared in a vision when the Winx used their Tracix wings in episode 16, but the Winx didn't go there until episode 17, when they went to free the Fairies of Earth. The island wasn't seen again until episode 24, when the Winx brought the Wizards of the Black Circle there for the trial. When Morgana put the Black Circle on her finger during the ceremony, as a sign of the capitulation and the submission of the Wizards to the justice of the Fairies, the Black Circle was destroyed and released dark energy which created a vortex in a large crack in the ground, which led to the Dark Abyss and would suck up all of the Earth Fairies, sealing them away for good and allowing them to take control of Earth. Luckily, the Earth fairies were all saved, and Nabu was able to close the chasm. Sadly, the dark magic had drained Nabu of all his energy, possibly resulting in him ending into a coma-like state (Morgana said that she would take care of him till he wakes up again). The Fairies of Tir Nan Og stopped trusting and being loyal to Morgana after this and started plotting against her and Nebula, blinded by her hunger for vengeance, overthrew Morgana, imprisoned her in a magical mirror and proclaimed herself as the new Queen of the Earth Fairies. She and Aisha, who joined her out of grief for Nabu, led the Warrior Fairies into the Omega Dimension to seek revenge from the Wizards who had fled there. At Tir Nan Og, the Winx and the Specialists had to fight the Warrior Fairies who had joined Nebula and were guarding the palace and finally found Morgana in the mirror. After revealing that Roxy was the only one who could free her since she was her daughter, Morgana, Roxy and the Winx went into the Omega Dimension and managed to convince all the Fairies to give up their revenge, except Nebula and Aisha. After failing to defeat the Wizards, Nebula and Aisha joined forces with the Winx and Roxy and finally defeated the Wizards. After this Morgana gave up her throne and decided to go live at Gardenia, with her family, for good. Morgana then named Nebula as the new Queen of Tir Nan Og after forgiving her and telling her that since she repented for her actions she was still on the side of good.
- The original island of Tír na nÓg, meaning the Land of Youth", features in Irish mythology as the place where the Tuatha Dé Danann, the previous inhabitants of Ireland (originally Divine and considered to be Gods, but later came to be regarded as Fairies), settled after the humans (the Gaels - the ancestors of modern Irish people) arrived in Ireland. It was said to be located in the Ocean far in the West, beyond the edges of the World and could be reached only after a difficult voyage or by being invited by a messenger of the Gods, that is of the Island's inhabitants, a Banshee (Banshees are fairies regarded in Irish mythology as messengers of the Otherworld and omens of Death, and act as messengers of the Gods to the humans).
- The Island of Tir Nan Og in Winx Club may also be having references from the mythical Island of Avalon (the Island of Apples) of the Arthurian Legend, which was usually associated with Morgan le Fay (who possibly inspired the character of Queen Morgana), who was supposed to live there with her eight sisters, as references to the Arthurian Legend have already been made when Faragonda was first telling the Winx Club the story of the Wizards of the Black Circle. According to legend, it was an enchanted island which would produce good things by itself such that it was not necessary to cultivate the soil, and fruits, cereals and other good things would grow by themselves. There, people would live a hundred years (which was unusually long in medieval times). It was supposed to be the place where King Arthur's sword Excalibur was forged, and where he was brought to rest following his final battle with his evil son Mordred and his apparent death, since it was said that he will raise again from the dead to lead his people against their enemies.
- The original Irish name is written Tír na nÓg and it is spelled "Teer na n-oh-g", unlike in the series where it is spelled "Tur nan Og".
- The Irish dub is the only dub that prenounces it properly.
- The island of Tir Nan Og is also used in the show, Huntik: Secrets and Seekers, which was also created by Iginio Straffi.