Fermanagh is excellent walking country. The Cuilcagh Mountain Park is readily accessible by road and provides challenging upland terrain but requiring only a short walk to summit the ranges. Limestone land around Florence Court and Derrygonnelly offers excellent limestone scarps. Think the English peak district without the people. The Forests of Fermanagh give fantastic public access and remote woodland walking. For gentle options or young children, there are excellent marked walks around the lough shore, forest visitor facilities and National Trust properties.
Best of all is just how clean the air is in County Fermanagh and walking fills your lungs full of it.