Errigal is a 751-metre mountain near Gweedore in County Donegal, Ireland. It is the tallest peak of the Derryveagh Mountains and the tallest peak in County Donegal. Errigal is also the most southern and the highest of the mountain chain called the "Seven Sisters" by locals. Wikipedia
has some of the highest sea cliffs on the island of Ireland. Although less famous than the Cliffs of Moher in Co Clare, Slieve League's cliffs reach almost three times higher. You can read more about it here.