There was a good report about visiting Cavan in Saturday’s Irish Independent newspaper, particularly the area around the river Erne (Ireland’s second longest river; both it and the Shannon, the longest river in Ireland, rise in County Cavan).
(Tipped by talktourism.ie)

Here’s a photo of the Bellavally Gap. Highest point in Glan Gap. Any water flowing left of here goes into the River Erne and on towards Ballyshannon, Co. Donegal; any flowing right goes into the Shannon, and on towards Limerick! The square shapes in the field the other side of the road are pieces of cutaway bog.