Bangor Erris gives easy access to Knocklettercuss and there is parking for hundreds at the GAA pitch which it literally a few steps from the start of the Bangor Trail. Thankfully its wetness is only followed for a short distance before climbing the slopes.

Even at this modest height views north are stunning, past the working quarry face on Carrafull to the North Mayo hills and cliffs and the waters of Broadhaven Bay. To the west a vast peatland carries the eye to the Atlantic and the iconic mountain shapes on Achill. As the 3 km summit ridge is reached the towering wind turbines to the east dwarf conifer plantations as they produce electricity for hundreds of thousands of households.

The walk to the summit is fairly relaxed with the landscape east and west constantly drawing attention. This hill keeps the views south as an enticement and when they finally appear they are worth the wait. The big mountains of the Nephin Begs rise splendidly out of further vast tracts of bog land with the long line of Slieve Carr dominant. Further south the jagged line from Corranabinnia to Glennamong creates a grand barrier. A cairn is passed on the way to the summit trig pillar. On a good day these views would be more than worth the effort. Today a brisk and cold easterly wind told me to keep moving.

As others have said an out and back return can be made to maintain the height or it would be handy enough to drop down west to pick up the Bangor Trail. I continued south with an approach to Slieve Carr as a focus. This crossed some of that tract of bog and it wasn't too bad after a relatively dry spell, though there was one 'floaty' bit that had me skirting around to be sure. On returning I did use the Bangor Trail which skirts the western flank of Letterknockcuss and it is very very wet going so be prepared for your boots to disappear at least once. Linkback: https://mountainviews.ie/summit/878/comment/23858/

I followed in the footsteps of Big Foot. Bangor is a lovely place with the feel of a wild west frontier town especially when you appreciate its isolation even more by looking down on it from the slopes of Knocklettercuss. The summit plateau is quite large. Goes on for almost a mile maybe before you hit the highest point. There's a large cairn on the way to the trig pillar whose silhouette beckons you from the horizon. Great view across to Slieve Mor to the west but the Slieve Carr massif dominates Knocklettercuss looming over it like some kind of forbidden mountain. Like Frodo on the way to Mordor perhaps. Well I turned back at this point. Maybe another time. Linkback: https://mountainviews.ie/summit/878/comment/6442/

Climbed 13.7.13 with Mrs and three kids. Parked at gaa pitch and headed along bangor trail. Similar to last comment turned up the slopes to top. Steep climb but very flat at top. Went down other side to Briska and back into Bangor. 4 and half hours. Linkback: https://mountainviews.ie/summit/878/comment/15039/

Done as a first step in a great circle route to make a weekend of it, bagging some new summits.
Start in or about Bangor Erris village, there's oodles of parking on the newly improved road in by the GAA club, and from here, follow the trail a short distance, and peel off left up the hill when the trail becomes wet, which it does rather quickly. The climb is easy, no great obstacles, and you can be at the top in an hour or so. There's a cairn and a trig a little distant from each other.
There's a trig and great views around, possibly an underrated or perhaps ignored Hill as most people will probably be doing the Bangor Trail if in this area. Linkback: https://mountainviews.ie/summit/878/comment/23985/