Enniskillen Castle, a former stronghold of the 16th-century Maguire chieftains, guards the western end of the town's central island, its twin-turreted Watergate looming over passing fleets of cabin cruisers. Within the walls you'll find the worthwhile, newly refurbished Fermanagh County Museum, which has excellent displays and interactive exhibits on the county's history, archaeology, landscape and wildlife. It includes a fascinating gallery dedicated to the history of Fermanagh's waterways as a route for pilgrims travelling via Devenish Island to Lough Derg in Donegal.
In the ground-floor Lakelands Gallery, look for the 1000-year-old 35lb block of bog butter, unearthed by a Fermanagh farmer in 1980; it was probably buried in the bog to preserve it for consumption during the winter months.
The 15th-century castle keep contains the Inniskilling Museum, full of guns, uniforms and medals, including eight Victoria Crosses awarded in WWI; it's dedicated to the regiment that was raised at the castle in 1689 to support the army of William I.