In Irish mythology, Tír na nÓg or Tír na hÓige is one of the names for the Celtic Otherworld. Tír na nÓg is best known from the tale of Oisín and Niamh.
The 'Land of the Ever Young' depicted by Arthur Rackham in Irish Fairy Tales (1920).
Oisín and Niamh travelling to Tír na nÓg, illustration by Stephen Reid in T. W. Rolleston's The High Deeds of Finn (1910)
Manannán or Manann, also known as Manannán mac Lir, is a sea god, warrior and king of the otherworld in Gaelic mythology who is one of the Tuatha Dé Danann.
Tír na nÓg
…meadows of the waters where the horses of Lir have their pastures." The god that rules this region in the surviving tales is almost always named as Manannán mac Lir. Other Old Irish names for the Otherworld include Tír Tairngire ('Land of Promise'/'Promised Land'), Tír fo Thuinn ('Land under the Wave'), Mag Mell…
Manannán mac Lir, sculpture by John Sutton at Gortmore, Magilligan, County Londonderry, Northern Ireland.
The boat from the 1st century BC Broighter Hoard, which was found near Magilligan and may be a votive offering to Manannán
Stephen Reid's illustration of the Sons of Tuireann in Manannán's boat
South Barrule, reputed home of Manannán on the Isle of Man