Lough Erne is not a lake. It is two lakes, a river, and somewhere around 154 islands, threaded together for fifty miles through the middle of the county like a flooded valley pretending to be a system. The Upper Lough is small and complicated, a maze of green inlets and reed beds where it is easy to lose track of which channel leads where. The Lower Lough is wider, deeper, more open, with islands such as Devenish and White Island where Christian monks built round towers in the ninth century and pagan stone figures stand in ruined church walls. Enniskillen, the county town, sits on a sliver of dry land between the two, and for centuries control of that sliver meant control of the only practical route between south Ulster and the west. The Erne was the boundary of Connacht and Ulster in the ninth century. It still feels like a border within a border.

Three upland areas frame the lakes. To the southwest of Lough Erne the West Fermanagh Scarplands rise to about 350 metres, a long limestone ridge that drops off sharply where the Cliffs of Magho overlook the lower lough. To the east, on the Monaghan border, the Sliabh Beagh hills roll up to 380 metres of blanket bog. To the south, along the Cavan border, the Cuilcagh mountain range crests at 665 metres, the county's highest point. The carboniferous limestone here, laid down 354 to 298 million years ago, has been hollowed into one of Ireland's great cave systems. The Marble Arch Caves snake under the western flank of Cuilcagh, with underground rivers, calcite curtains, and chambers tall enough to lose your voice in. Older still are the red beds north of Lough Erne, 550 million years of sediment from a continent that no longer exists.

Fermanagh was Maguire country for nearly four hundred years. Donn Carrach Maguire became the first recognised chief of the dynasty around 1264, and his successors held the lakelands and their portage routes through the medieval centuries. The Annals of Ulster, which covered medieval Ireland from AD 431 to 1540, were compiled at Belle Isle on Lough Erne. The Maguire grip began to slip in the Nine Years War at the end of the 1500s, and after Hugh Maguire was killed in 1600 and Ulster's Irish lords fled in 1607, Fermanagh was carved up. The baronies of Knockninny and Magheraboy went to Scottish undertakers, those of Clankelly, Magherastephana, and Lurg to English ones, and the rest was parcelled out to crown servitors and to a few surviving native families. The chief beneficiaries, the Coles, the Blennerhassets, the Humes, the Dunbars, are the names you still see on Georgian gateposts.

When the Great Northern Railway closed its lines through Fermanagh in October 1957, the county became the first non-island county in the UK without a railway service. It has not regained one. That absence has shaped Fermanagh more than most outside observers notice. The county slowed, depopulated, lost industry, and turned, eventually, to the lakes and the caves and the National Trust estates for whatever future it could find. The Trust now manages three properties here: Crom, a romantic ruined-castle estate of 1,900 acres on the upper lough; Florence Court, an 18th-century mansion eight miles outside Enniskillen with one of the great walled gardens of Ulster; and Castle Coole, a Wyatt-designed Palladian palace built in 1797 from Portland stone that arrived by barge. Fermanagh has become the holiday county. The slowness that emptied it is now the thing people pay to come and feel.

Fermanagh borders five other counties: Tyrone to the northeast, Monaghan to the southeast, Cavan to the southwest, Leitrim to the west, and Donegal to the northwest. Three of those borders, the ones with Monaghan, Cavan, and Donegal, are international, marking the line between the United Kingdom and the Republic of Ireland that was drawn in 1921 and that ran through the lives of every Fermanagh family in the decades that followed. The 1981 by-election in Fermanagh and South Tyrone elected Bobby Sands, a Provisional IRA hunger striker, as MP weeks before he died in the Maze Prison. The G8 leaders came to Lough Erne in 2013, partly because by then Fermanagh was safe enough, beautiful enough, and quiet enough to host Cameron, Obama, Merkel, and Putin in one resort hotel. The county that did not behave had become, on the surface at least, the county that does not raise its voice.