Summerlands?
Tír na nÓg; "Land of the Young" or "Land of Youth" depicted as a paradise and supernatural realm of everlasting youth, beauty, health, abundance and joy. The inhabitants enjoy a life of eating, dancing and loving and they never have to deal with death or dying. Its inhabitants are the Tuatha Dé Danann. In the adventure and voyage tales, various Irish mythical heroes visit Tír na nÓg after a voyage or an invitation from one of its residents (The Voyage of Bran for example) . They reach it by entering ancient burial mounds or caves, or by going under water or across the sea.
Also...
Tír Tairngire; "Land of Promise/Promised Land"
Tír fo Thuinn ; "Land under the Wave".
Mag Mell; "Plain of Delight/Delightful Plain".
Ildathach; "Multicoloured place".
Emain Ablach; the Isle of Apple Trees
Annwn.
Fairyland.
Hy Brasil.
The Celtic Otherworld.
The Voyage of Bran
(Link)
https://m.youtube.com/watch?v=AQ8xP_Z8q0E