Complex sentence: Dunree Fort, on the west side of the Inishowen peninsula in the north of Ireland is a Napoleonic period fort mounting 8 guns on a rocky promontory accessed over a natural fissure.
Split into simpler sentences: Dunree Fort, located on the west side of the Inishowen peninsula in the north of Ireland, is a Napoleonic period fort. The fort is located on a rocky promontory accessed over a natural fissure.