The Bangor Trail is an old road through the Nephin Beg mountains in north-west Mayo. It used to be the main route from Bangor to Newport, dating back to the 16th Century. Nowadays it mainly attracts recreational walkers, though due to the distance involved and the rough ground underfoot it is probably quieter now than it once was at the height of Ireland’s population in the early 1800s.
The Bangor Trail is one of the toughest hikes in Ireland, taking an average of 10 h 18 min to complete. This trail is great for backpacking, camping, and hiking, and it's unlikely you'll encounter many other people while exploring. The best times to visit this trail are April through October. Here is an excellent review of hiking the Bangor Trail.