One way up this Maumtrasna outlier is from the Coillte forest entrance near Derrinkee Bridge at M011 725 A, 15km south of Westport. Follow the track into the forest until it comes alongside a fence at forest edge, overlooking a river, cross the fence and river (likely to be impossible when in spate) and head roughly SE across the bog to reach a moderately steep grassy slope. The slope soon levels off and you climb gradually to the southwest, over undulating ground, keeping the steep edge in sight to the right. The summit plateau is soon reached, where there are a few contenders for the highest point, as well as a number of lakes and a nice view from the edge down over the impressive corrie lake of L. Glenawough. This is not a place to be in the mist, so be sure to navigate carefully.
An alternative approach is to start at the end of a minor road at M030 695 B, just past farm buildings. A kind farmer was happy to permit access up the hillside and suggested driving a further 50m beyond the end of the road along a stony track, where there is space to park and turn beside the ruin of a cottage. Head directly up the steep hillside to the right, which is the only steep part of the ascent and takes you to over 300m elevation. Turn SW and continue in that direction for 3.5km. The varied terrain is a mixture of grass, rock, boggy patches and peat hags, but the ascent is mostly gentle. The broad summit is marked by a small pile of stones (pictured). 1.5 hours to summit. Linkback: https://mountainviews.ie/summit/421/comment/5180/

Just south of Barnahowna this impressive glacial valley stretches towards Lough Mask. By coming into this valley from the vicinity of Killateeaun (in mist at top of pic) it should be possible to reach the col between Maumtrasna and Barnahowna affording access to either. The col is at L996 670 C and is near where this picture was taken . I haven’t tried it but one way would be to go to the west end of the forest shown below and walk NE along a narrow path that exists along a decayed fence above the trees to the col. Or perhaps start from the east end of the forest though it looks very steep. Or go through the forest (a single ride is shown on a satellite picture from about 2000 going directly through the forest immediately south of Barnahowna – but that can hardly be guaranteed.) Linkback: https://mountainviews.ie/summit/421/comment/1675/

One way to reach Barnahowna is as part of a grand walk starting from the middle of the Partrys. From Tourmakeady take the road east over the range, turning off to reach a point on a minor but passable road at around M027705 D. Between you and the route to Barnahowna are various fields which when I passed in late April one year were full of noisy sheep and lambs. Avoid the farming by walking west on the road and turning north east at its end onto a rough track which leads towards forestry. From here rough moorland stretches to Barnahowna.

At around M018700 E you can see the view below of the stumps of a long gone wood. Walk about SW over the rough ground to reach the summit nearly 3k away. Linkback: https://mountainviews.ie/summit/421/comment/1672/

Right beside the summit is what I take to be Lough Naweelion. The label on the 1:50k map seems to describe a much smaller lake 200m north but presumably it is meant to refer to the larger lake below which irregularly extends some 220m.

Now it’s a pretty unusual sight to see a lough of this size right on top of a mountain and it’s even more unusual to find a construction like the one in the picture on an island in the lake. At first I thought it was some quixotic cairn that someone had built, so near is it to the summit. (It turns out to be only about 1.5 metres below the summit which is 150m away) Then I considered ancient monuments and other increasingly improbable explanations. By hopping from island to island over some stepping stones you can reach it. It’s a ring of stones about 70cm high. Most probably it’s a hide for someone shooting wild fowl, at least there was a spent shotgun cartridge there. Linkback: https://mountainviews.ie/summit/421/comment/1673/

Two of the huge coums that dominate the sides of the Partrys nearly meet at the col between Barnahowna and Maumtrasna. At the lowest point of the col I found this simple memorial which says

In Memory of

THE MAN WHO DIED

HERE DURING THE

FAMINE YEARS

R.I.P.

The lake behind this stark reminder of our past is Lough Glenawough, at about 1170m long, the longest of the corrie lakes around Maumtrasna. Linkback: https://mountainviews.ie/summit/421/comment/1674/

I reached Barnahowna from the south-east, from a spot marked on some maps as "Glensaul Loop Trailhead", M04117 63978 F. There is just enough space to park a car here by the hairpin bend without blocking the road or access to the dirt track.

Follow the track for about 3k, you will have great views of the Maumtrasna range in the distance and, much closer to you, a waterfall just ahead in the valley you're approaching. You're aiming for the ground above the waterfall which looks deceivingly inaccessible from here. When you reach the plateau and the track starts petering out, around M03281 66137 G, leave it and cross a boggy section to reach slightly firmer ground. From here it's a bog slog until you get to the cairn that marks the summit.

The ground was firm enough when I crossed the boggy plateau in late April but navigation might be tricky and the easiest route back is retracing your steps.

Unfortunately I couldn't check if the col at L996 670 C mentioned by simon3 can be easily crossed as it wasn't visible from where I was and I didn't fancy crossing more metres of bog to get a better view of it.

The walk took just over 4 hours at a moderate pace, 16k round trip. Linkback: https://mountainviews.ie/summit/421/comment/20519/