The most likely access to Knockacullion is from Bencroy or Slieve Anierin. We don't have information on reaching it from the west, Lough Allen side or the East side where there is a substantial cliff.
The summit is fairly flat on all sides except to the east and is covered in more or less unbroken blanket bog. The top has a distinct well established pond.
Please note that approaching from north or south you are walking on trackless moorland which many commentators have noted as sapping energy and taking an unexpected amount of energy. Linkback: https://mountainviews.ie/summit/337/comment/5097/

Knockacullion, in keeping with most of the hills in the area, has a dull summit area but more than makes up for this with the impressive cliffs stretching along the SE of the hill. Walking along the tops of the cliffs and those of Slieve Anierin is a fantastic experience for over 3 km. I approached the hill from Bencroy (a natural route which shows three hills in thier best light), descending to the col over quite a wet area, past a pool of water and making for a long low ridge with a rocky side lifting it above the ground below. This ridge can be followed to the summit area and then the line of cliffs can be followed towards Slieve Anierin, as contour around the hill Lough Nabellbeg comes into view, nestled perfectly below the start of the cliffs to Slieve Anierin and glistening in the sunlight very invitingly. There are cracking views S & E over the lowlands with numerous loughs. There is a slight drop down to the col before the ascent of Slieve Anierin. On the return from S Anierin I dropped down steeply at this col to the base of the cliffs and walked along the bottom back towards Bencroy. There has been a very substancial landslide in the not too distant past - can be clearly seen in the photo and has swept all before it for a considerable distance - are some more minor slides further along. A really nice hill which plays it part perfectly in the round of this walk. No one else up top on this trip. Linkback: https://mountainviews.ie/summit/337/comment/2392/

Climbed February 20th 06. Accessed from Slieve Aneirin (first part of walk). From summit of Slieve Aneirin I took a bearing of 48 degrees NE to take me safely onto the col (H028169 A) south of Knockacullion. Thankfully, the mist cleared as I approached the col, providing me with a clear view of my target. The col between Aneirin is, once again, quite marshy with fairly long trussock grass and gorse to negotiate making the going tougher than it might first appear (or maybe my early morning start was catching up with me). In any event I reached the relatively flat and featureless summit, (that is featureless apart from it’s locheen), in brilliant sunshine. The early morning mist had all but burned away, lingering only (as it did all day on Cuilcagh to the north-east) but haze hindering long distance views/photography. Nevertheless there are lovely views north over a fertile valley to Slievenakilla and west towards Lough Allen. I was intending to take a break on the summit but due to the lack of suitable ‘dry’ seating and the nearness of Bencroy I decided to postpone the break making do with a Mars bar 'on the hoof' as I descended the northern slope of Knockacullion. (See Bencroy for final part of walk). Linkback: https://mountainviews.ie/summit/337/comment/2193/

Climbed from Bencroy. Best route is to get onto the higher edge of Bencroy, via the path that leads to the old quarry (right fork off the main path) and head for the obvious ridge that leads to Knockacullion. By coincidence I followed the same whitish, rushy "path" mentioned by eflanaga, even though I had not read his comments before I climbed. While this is a bit wet and soft in places, it is a much better alternative to the high heather and wet bog that lie in the more direct route, which should be avoided except you are in the mood for hardship. The top is featureless except for a small lake - see photo, with Slieve Anierin in the background. There are great views of all the surrounding hills and you can clearly see well into Sligo on a good day - Knocknarea was visible when I was on top. The highest point is about 30 metres West of the lake. Linkback: https://mountainviews.ie/summit/337/comment/3138/

The day we were there it happened that rain was receding north and there were views to the west. The picture shows Knocknarea and Queen Maeve's Tomb at around 290 degrees bearing on the skyline and 47.2km distant. To the left and on the skyline is Slieve Daeane and the rising ground to the right is Killerry Mtn. Also partially visible was Nephin Linkback: https://mountainviews.ie/summit/337/comment/20864/