The name comes from the Irish word Cuilceach, traditionally translated as 'chalky.' The mountain is mostly sandstone and shale, covered with bog and heather, so 'chalky' looks misleading on first inspection. But the cliff-edged summit is formed of the hard-wearing Lackagh Sandstone, which overlies the Briscloonagh Sandstone. The name may refer instead to the limestone rocks on the lower northern flanks: the Glencar and Dartry Limestone formations, where streams disappear underground at the swallow holes that feed the Marble Arch caves. If so, the meaning is 'calcareous' rather than chalky, which fits the geology. The mountain was sometimes called Slieve Cuilcagh in English; 'Slieve' is an anglicisation of Sliabh, the Irish word for mountain. In the 1609 Plantation of Ulster, Cuilcagh was part of lands granted to John Sandford of Castle Doe by letters patent dated 7 July 1613. Sandford later sold the land to his wife's uncle Toby Caulfeild, 1st Baron Caulfeild, Master of the Ordnance, in a sale confirmed by letters patent on 12 July 1620.

The Cuilcagh Mountain Park was opened by Fermanagh District Council in 1998. In 2001 it joined with the popular Marble Arch Caves and the Cladagh Glen Nature Reserve to form one of the first UNESCO-recognised European Geoparks. The Cuilcagh Mountain Ramsar site, designated under the Ramsar Convention for wetlands of international importance, covers 2744.45 hectares of the mountain's blanket bog, including some of the most important upland insect habitat in Ireland. Water beetles with formidable names: Agabus melanarius, Agabus arcticus, Dytiscus lapponicus. Water bugs called Glaenocorisa propinqua and Callicorixa wollastoni. Lough Atona is the main locality for many of these species. The mountain is also Ireland's 170th highest peak, a modest ranking for a hill with such an outsized hydrological influence.

Then a boardwalk happened, and everything changed. Starting from the Legnabrocky Car Park, a trail over six kilometres long runs to the mountain's upper reaches. The first five kilometres climb gently on a wide gravel track. The final kilometre is the now-famous part: 450 wooden steps mounted on a boardwalk, climbing up the steep upper slope to a viewing gallery near the summit. The boardwalk was originally laid down to protect the fragile blanket bog from being chewed up by walkers, but its dramatic photogenic profile, a zig-zag of timber stretching up into the sky, turned it into a social media phenomenon. Irish Independent dubbed it 'Ireland's own Stairway to Heaven' in April 2017, and visitor numbers exploded. The popularity led to concerns about the area's ability to handle the increased footfall, and walkers are now advised to allow two and a half to three and a half hours for the full 12-to-14-kilometre round trip.

What makes Cuilcagh genuinely unique is how its waters split between two destinations. Streams on the southern slope sink into the limestone, travel underground for miles, and emerge at Shannon Pot in County Cavan, the traditional source of the River Shannon, which then flows 360 kilometres south through eleven Irish counties to empty into the Atlantic at Limerick. Streams on the northern slope similarly disappear into Cats Hole and the other named swallow holes, join underground to form the Owenbrean, the Sruh Croppa and the Aghinrawn rivers, and emerge as the Cladagh River at a natural rock bridge known as the Marble Arch. The Cladagh then flows north into Lower Lough Erne and eventually out to the Atlantic via the River Erne at Ballyshannon. Two mountains' worth of water, two of Ireland's great river systems, and one ridge of sandstone deciding which direction each drop takes.

Walking the boardwalk on a clear day you can see Benaughlin to the north, the rest of the Fermanagh hills stretching east, and on a really clear day the distant Atlantic to the west. The international border runs invisibly across the upper slope. Cross it on the boardwalk and you have moved between currencies, customs jurisdictions and, since Brexit, the European Union itself. But on the ground there is nothing to see: just blanket bog, peat hags, heather, and the constant Atlantic wind that has shaped this landscape since the last glaciers retreated. Cuilcagh is a quiet mountain. Even at the busiest tourist weekends, by the time you reach the upper boardwalk the crowd has thinned, and the view from the viewing gallery extends across two countries and an entire continent's worth of weather patterns blowing in from the west. For a hill of only 666 metres, it carries an unusual amount of geography on its shoulders.