As Niamh had promised, Tír na nÓg knew no sorrow, no one went hungry or thirsty, and everyone lived forever. Niamh and Oisín were married, and lived for many years happy together, although a small part of Oisín missed Ireland and his father, and the Fianna.
Soon enough, the longing grew in Oisín to return to Ireland, and he begged Niamh to let him return. Niamh was reluctant, because she knew the danger of Oisín returning to Ireland, and that she would never see her husband again. Niamh saw how much Oisín missed his family, and, because she loved him so much, she agreed to let him return and see them. She gave him her magical white horse, Embarr, and, before leaving, warned him not to get off the horse, or to let his feet touch the ground, for, if he did, he would be unable to ever return to her in Tír na nÓg. This Oisín promised.
Oisín set off across the sea on Niamh’s horse, and soon arrived in Ireland. But things, he could see, had changed. What Oisín didn’t know was that time moved more slowly in Tír na nÓg, and what had seemed like only a few short years had been 300 years in Ireland. The Fianna no longer rode the countryside hunting, and the castles and homes they all lived in stood in crumbling ruins.