Beinn Mhanach is a dome-shaped and unspectacular Munro. One of the remoter peaks of the Southern Highlands, it does have a feeling of seclusion and the approach up the glen from Auch is very enjoyable.
There are no paths on Beinn Mhanach. The approach up the glen is on a good track but fords the river several times, which may not be possible in spate.
Buses run along the A82 past the start.
A82 near National Park boundary.
There is limited parking on the east side of the A82 just north of the sign for the Loch Lomond National Park boundary. The walk begins along the track heading north from here, with great views ahead of Beinn Dòrain. Soon the West Highland Way joins in from the right. Continue ahead along it until the track reaches a cross-roads. The West Highland Way continues ahead over a bridge here; but to continue for Beinn Mhanach don't cross, instead turn right alongside the Allt Kinglas.
The track crosses a bridge over the stream coming down from Glen Coralan on the right before passing beneath the railway viaduct and entering Gleann Ach-innis Chalein, more commonly known as the Auch Glen. When the track forks, keep to the left branch close by the river. The track soon fords the river, crossing to the north side. This can sometimes be done with dry feet but when in spate could be quite impossible. Continue on the far side until the track recrosses the river at a second ford around 1.3 kilometres further on (continuing on the near side would be possible but rough and boggy).
The track now crosses several shallower bends in the river before crossing back to the north side again at NN350386. This time it stays on the north side for only a short distance before crossing back, and there is a path remaining on the south side. Finally after the river forks the Allt a 'Chùirn branch is forded to reach the farm buildings at Ais an t-Sìdhean. The great Gaelic poet Duncan Ban MacIntyre lived here in the eighteenth century; he celebrated the beauty of Beinn Dòrain on the left in his most famous poem.
The track fords the river again before crossing it a final time at - a bridge made of sleepers! Just beyond it forks; take the right hand branch which heads up the glen to the east. After around a kilometre the track crosses a bridge over the Allt a'Chùirn which here descends steeply from the hillside on the left, with a series of waterworks which extract water for the hydro-schemes of Perthshire. Cross the bridge and then leave the track, heading straight up the hillside to the left, keeping to the right of the stream. A fence also runs up the hillside a little to the right - this leads to the bealach between Beinn a'Chùirn and Beinn Mhanach.
The easiest going is by crossing the fence part way up to aim directly for the latter summit. The ascent is unrelenting but the going is grassy and mostly firm. The summit of Beinn Mhanach is a Munro at 953 metres. There are higher peaks all around restricting the view, with Beinn a'Chreachain to the north looking the most impressive; a short detour further along the ridge brings most of Loch Lyon into view. The easiest and quickest descent is to retrace the outward route. There is a reasonable alternative which crosses wetter and slightly rougher ground. This descends to the bealach with Beinn a'Chùirn (a Top, which can be visited by a short detour from this point though its other slopes should be avoided). Here the fence will be rejoined, and can be followed across the boggy hillsides towards the lower bealach of Lon na Cailliche at NN354417.
Head down the glen of the Allt an Loin from here. A track will soon be picked up that crosses the stream twice before forking. Keep left here before re-crossing the stream beneath a small concrete dam. The track then descents to rejoin the outward route at NN357395. From here retrace your steps down the glen, eventually passing back under the viaduct to return to the start.
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