Tir No Nag?

Yes.

You've spelt it wrong.

It's Tír na nÓg.

Roughly translates to country of youth.

You havn't asked anything specifically and I can't write the whole story here so this is about all my answer will be.

I have just checked, the wikipedia article is accurate, albeit only a brief summary:

http://en.wikipedia.org/wiki/Tir_na_nog

The tale of Tír na nÓg generally refers to the tale of Oisín and Niamh. It is the final paragraph of the link above.

Oh, by the way, it's Tir-na-nOg, not "Tir No Nag".

And it's not a tale at all - what it means is "The Land of Youth". The term refers to the Otherworldly Paradise, which lies somewhere to the West.

The inhabitants of Tir-na-nOg never grow old. It is a land of eternal summer, full of beautiful flowers, wells and springs, flaming trees, music, joy, song and laughter and lovely maidens, and there is no sorrow, death or disease.

Irish heroes often enter this Otherworldly paradise, the most famous examples being Cuchulain and Oisin. There is no "Rip van Winkle" story associated with Cuchulain, but there is certainly one with Oisin, who goes off with Niamh of the Golden Hair. When he returns to the real world, he finds out that all his friends & relations have gone. Time passes much slower in Tir-na-nOg.

In Arthurian legend, you may have known Tir-na-nOg as Avalon, or Ynys Avallach (Isle of Apples), or Emain Ablach, or the kingdom of Evelake (Avallach). "Evelake" relates Tir-na-nOg to the Castle of the Grail, Castle Corbenic (Castle of the Blessed Horn), or the place where a Cauldron of Plenty exists. One such magical Cauldron is listed in the Thirteen Treasures of Britain as "The Cauldron of Diwrnach"; the Horn of Bran is also listed there. Like the Grail, both the Cauldron of Plenty & the Blessed Horn could grant as much food & drink as one desired - and eternal life.

Therefore, one other name for Tir-na-nOg was Annfwn (Welsh). Arthur and his knights raided Annfwn to steal the magic cauldron of Diwrnach. It is possibly the same place called "The Isle of Glass" that Merlin retired to with the Thirteen Treasures, and also Avalon, where Arthur was taken to be healed after the Battle of Camlann.

Tír na nÓg

Tír na nÓg is the fabled island off the west coast of Ireland "The land of perpetual youth" where the Tuatha de Danann (the Sidhe) resided. It also was home to a few mortals who were carried there by the Sidhe such as the Celtic hero Oisín who loved the ban-sidhe (fairy woman) Niamh and lived on the island for what he perceived to be a year. Time on Tír na nÓg seemed to pass at a different rate to time on earth. Hence when Oisín returned to his homeland to visit his family and friends he discovered that they were all long dead and three hundred years had passed by.

Other names for Tír na nÓg are Oilean na mBeo - the Island of the Living, Tír na mBuadha - the land of Virtues, Hy na Beatha - the island of Life, Tír na mBeo - the land of the Living and Hy Brasail - Brasil's Island, The Land of Promise, and the Land of Youth. Also known as the Land Over Sea, and the Land Under-Wave.

Time stopped still on Tír na nÓg, one never grew old or suffered from any illness, it was always of a temperate climate neither too hot nor too cold. The flowers bloomed perpetually and never died. There was no sorrow or pain, love was eternal it was without wars or famine or any of the ills of the earth.

To get to Tír na nÓg it was necessary to cross a stretch of water and then to go under the waves for a time before coming again to dry land. The 'horses' of the sidhe crossed the waves as if they were a solid surface.

People have been fascinated by the legend of Tír na nÓg for countless generations. During the twelfth century Giraldus Cambrensis tells the story of how an island appeared suddenly off the west coast of Ireland but when people tried to approach and land it immediately vanished. A group of people went out again in search of the island and having steered within bowshot of it struck the island with a red-hot arrow in consequence the island immediately remained stationary.

It has long been the subject of poetry and bardic literature. In 1853 the Ossianic Society was founded by Mr. Hardiman and Mr. O' Flanagan and others to preserve and collect all literature and poems regarding the legendary heroes Fionn mac Cumhaill, Oisín and Oscar and the land of Tír na nÓg

the mythical otherworld paradise