This is Ben Bulben, in Sligo.  It is mentioned in several of Yeats' work and also in the Irish Legend of Diarmuid and Grainne.

    Diarmuid and Graine were two young lovers.  They met at Grainne's pre-wedding banquet.  She was supposed to marry Finn, an older man, over twice her age.  She had to interest in marrying him and chose Diarmuid to be her lover as soon as she saw him.  She filled a cup with wine, then put a curse on it.  As was custom, her husband to be had a drink, then passed it around the table.  One by one the party fell asleep.  When it was Diarmuid's turn, she kept him from drinking by kissing him. Then she propositioned him and the two ran off together.

    The ran off through the woods and became lovers, who in turn were also wanted by Finn, who was very upset at his young bride-to-be.  One day, under Ben Bulben, Graine had a craving for berries and Diarmuid went to fetch her some.  Bad luck, I'm afraid as he was picking the berries he was attacked by a wild boar and killed.  A devastated Graine returned to her kingdom and married the awaiting Finn (wasn't too devastated, was she)?