I once did the Glencoaghan Horseshoe in the 12 Bens, starting and finishing by the Ben Lettery youth hostel on the N 59.
I remember it being quite rough going in places with a lot of ascent/descent and navigation a bit tricky under poor visibility. It was a fine walk though and despite it being the middle of summer and not a bad day for it, and that youth hostel was fully booked (I stayed at Clifden the night before)...I did not see another person during the walk.
I have got a book (Lonely Planet Walking in Ireland), with a route description of this walk.