Overview
The Gleniff Horseshoe is a compact 10 km circuit on the northern edge of the Dartry Mountains in County Sligo. It’s one of Ireland’s most accessible glacial valleys, offering a seamless blend of driving, cycling, and walking. The single-lane road snakes clockwise through a dramatic U-shaped trough, flanked by vertical limestone cliffs and open moorland. The route delivers uninterrupted views of Truskmore, Tievebaun, and Benwisken, with Donegal Bay visible on clear days.
How the Valley Formed & Local History
The valley’s dramatic shape is a direct result of the last Ice Age. Glaciers over a kilometre thick carved through the Dartry range, scouring out the deep trough that defines the horseshoe today. Long before the ice retreated, the valley floor supported a dense Mesolithic forest of hazel, ash, and oak, attracting early hunter-gatherers.
By the 19th century, the focus shifted from timber to stone. The Gleniff Barytes Mill, located beside the river at Annacuna, became a busy industrial hub. Workers extracted barytes (a heavy quartz-like mineral) and shipped it via a private railway to Mullaghmore harbour. The stone foundations, water channels, and a short woodland trail remain today, offering a quiet reminder of the area’s working past.
Local lore adds another layer to the landscape. According to Fenian legend, Diarmuid and Gráinne fled the wrath of Fionn mac Cumhaill and took refuge in a high cave on the slopes of Truskmore. Known as Diarmuid & Gráinne’s Cave, it sits high on the cliff face. While it’s a striking landmark visible from the road, the approach crosses private land and involves steep, unstable terrain. Visitors are strongly advised to admire it from the valley floor rather than attempting the climb.
Walking & Driving the Loop
The route works equally well as a scenic drive, a cycling route, or a hiking trail. The road itself is quiet, largely traffic-free, and takes about 25–30 minutes to complete clockwise. Cyclists will appreciate the smooth tarmac and minimal traffic, though the narrow lanes require caution when passing farm vehicles.
For walkers, the Benwisken Trail follows much of the horseshoe road, extending into a 13.6 km moderate loop that takes around four hours. It connects the Barytes Mill site with the Benwisken Centre, passing waterfalls, ancient field walls, and open upland paths. A shorter 9.1 km alternative starts directly from the mill car park, winding through native woodland and alongside the stream – ideal for a relaxed half-day outing or a picnic stop.
Key Stops & Highlights
- Gleniff Barytes Mill: The starting point for most visitors. The car park features information boards, and a short trail follows the old mill race through a small gorge with a cascade.
- Annacuna Cliffs: Towering limestone faces that drop vertically into the valley. The geology here is clearly visible, with distinct sedimentary layers telling millions of years of geological history.
- Diarmuid & Gráinne’s Cave: Look for the dark cave mouth high on the eastern cliff face, visible near the old schoolhouse site.
- Magic Hill: A short signposted turn-off reveals a gravity hill where perspective tricks the eye. Put a car in neutral or roll a ball, and it will appear to move uphill against gravity.
- Dolmen: A small, well-preserved megalithic tomb sits on the eastern side of the loop, surrounded by a ring of stones. It’s a quiet spot that underscores the area’s deep Neolithic roots.
Wildlife & Flora
The horseshoe sits in a transitional zone between lowland pasture and upland moorland, supporting a varied ecosystem. Mountain hares are a common sight on the open slopes, while kestrels hover over the grassy verges. Peregrine falcons use the limestone cliffs as nesting sites, and red deer are occasionally spotted along the tree lines. In spring, the hedgerows and damp hollows fill with bluebells, primroses, and wild garlic. Autumn brings a carpet of bracken and heather turning copper and purple, making it a particularly photogenic time to visit.
Practical Tips for Visitors
- Getting there: Exit the N15 at Cliffoney and follow signposts to the Gleniff Barytes Mill. The route is clearly marked throughout.
- Parking & Facilities: Free parking is available at both the Benwisken Centre and the Barytes Mill site. There are no public toilets or shops on the loop itself; plan to use facilities in Cliffoney or Mullaghmore before setting out.
- What to wear: Upland weather shifts quickly. Even on mild days, bring a waterproof layer, sturdy walking shoes, and a light windproof jacket. The higher sections offer little shelter.
- Safety: Stick to the designated paths and road. The cave approach is on private land and poses a serious fall risk. If you venture off the main route, tell someone your plans and carry a fully charged phone. In an emergency, contact the Sligo-Leitrim Mountain Rescue Team.
- Best time to go: Spring and early autumn offer the most reliable weather and vibrant scenery. Winter daylight is limited and the road can ice over, so check conditions before heading out.
Nearby Attractions
- Carrowkeel Megalithic Complex: A short drive north to one of Ireland’s finest passage-tomb sites, set beneath the Cúil Íorra Peninsula. (Carrowkeel)
- Benbulben Forest Walk: A 7 km loop around Sligo’s iconic flat-topped mountain, offering woodland trails and coastal views. (Benbulben Forest Walk)
- Ballygilgan Nature Reserve: Located a few kilometres west, this coastal reserve is excellent for spotting waders, seabirds, and migratory species. (Ballygilgan Nature Reserve)