The Fortunate Isles are located somewhere in the Western Ocean – beyond sunset, as Tennyson would say – and it’s where you go if you were a particularly great hero or otherwise favoured of the gods.
As with most Heavens, they feature boundless varieties of beast and bird. Unlike most Heavens, at least according to Pliny, “are greatly annoyed by the putrefying bodies of monsters, which are constantly thrown up by the sea” – not a common feature, and possibly indicative of some lack of favour on the parts of either Mannanan Mac Lir or Poseidon.
If you can get past the occasional smelly monster corpse – surely no worse than any beached whale – the Fortunate Isles are indeed a fine place to be (or after-be). Plus, they have possibly the most superb sunsets of any known life or afterlife.