Tir Nan Og College is the school for Earth Fairies. Nebula turned her tower into the school. According to the Tome of Magic History, the only solution in locking the Legendarium is in Tir Nan Og. This must mean that Eldora traveled around the world, including Earth, before the Winx returned magic to Earth and freed the Earth fairies.
The college still looks like the palace. But it is revealed that there is an underground chamber where the magic history can be found, which includes the Mythix Wands of the ancestral fairies, who traveled from the Legendarium World to the real world.
The students of Tir Nan Og College wear similar uniforms. They wear green capes that are tied on their chest. The edge of their rosy pink uniform has green lace. They also wear v-cut, pink skirts which has a darker shade of pink at its edge.They also wear sandals that has vine-like laces that are connected from her knees to her shoes.
In "Mythix," the Winx and Eldora go to Tir Nan Og College to find the key to the Legendarium. With the aid of Nebula, Queen of the Earth fairies, and her fairies, mostly of Bloom, they stop the Trix from conquering their school which proved their worth to the Ancestral Wands and earned their Mythix power.
In issue 133, The Winx, along with Morgana, decide to sit in on one of Nebula's classes at the Tir Nan Og College, and find that two young fairies, Lydia and Nadine, have become skilled in casting illusions. Strangely enough, Nebula is enraged by this and has the two girls expelled upon seeing this, and the Winx quickly learn that Nebula has been harboring a deep-seated fear of illusion magic ever since she had been defeated by Yllidith, the Lord of the Fairy Hunters, during a terrible event in the middle of the Great Fairy Hunt. Things begin to take a turn for the worst when Yllidith breaks free from his imprisonment having tricked Lydia and Nadine into breaking the seal that had been keeping him back. Now freed, Yllidith begins to exact his revenge on the Earth Fairies by trying to destroy the College! And, as the Winx figure out a way to stop the evil wizard, Nebula needs to overcome her fears if they wish to stand any chance.
Just as the student had reported, the Winx and Morgana find both Lydia and Nadine in the school's basement, scared and panicked over a mysterious professor becoming enraged with them having people follow them to another one of his lessons. The two beg for Morgana not to punish them and Morgana promises the possibility of overlooking their actions so long as they come clean and tell them the truth. And so, when asked of this professor's identity, the two Earth Fairies reveal that he is a strange man who lives in the basement and never shows himself, but rather teaches them by using telepathy.
The two of them had actually run into the professor by accident when they wandered into and quickly got lost in the basement. From that day forward, this professor had taught Lydia and Nadine how to strengthen and concentrate their magic better by having them channel it into a strange M-like seal on a nearby broken pillar. Seeing the nearly-broken seal causes Morgana to panic once she recognizes it as the same seal she had created to keep Yllidith imprisoned. Confused by the former high queen's reaction, Lydia questions what she means, only for her and the Winx to reveal to her and Nadine that their professor was none other than Yllidith, who projected into their minds and used them to break the seal and set him free. Though, just when Nadine realizes that they had been tricked, a voice cries out from behind Morgana over how they are now free to exact their revenge on both her and all of her fairies.
Yllidith then uses his magic to cause the College to shake and break down, which naturally causes all the students to fly into a panic. Nebula tries to get the Winx to flee with her until Tecna reveals that her computer is able to see through it all; that the collapse of Tir Nan Og College is nothing more than a large-scale illusion of Yllidith's creation. Nebula find herself unable to completely believe in Tecna's findings due to the realism of the illusion and, as Bloom tries to get her to face her fears, Yllidith attacks Tecna, destroying her computer to keep them from seeing through his illusions again.
With another encouraging push from Bloom, Nebula finally finds the strength to break free of her fears and releases a wave of magic that dispels of the wizard's illusions. Yllidith admits to being impressed with Nebula's growth but remains prideful in his belief of being undefeatable as Nebula still cannot face him without Morgana or the other Major Fairies.
With Yllidith now gone, Musa regroups with her friends while supporting a recovering Morgana. Morgana goes on to praise the Winx and Nebula for their efforts, specifically expressing how proud she is of Nebula for proving yet again that she deserved to be her successor. Nebula, now mostly done with cowering in fear at the very mention of illusions, turns to praise Lydia and Nadine for their magical replicas as their appearance acted as the pivotal moment in finally doing away with Yllidith. In addition to removing Lydia and Nadine's punishment, Nebula removes the ban on illusory magic from the school and encourages both them and any other curious Earth Fairies who wish to learn and improve on creating illusions.