Complex sentence: Shanbally Castle was built for Cornelius O'Callaghan, the first Viscount Lismore, in around 1810, the mansion was the largest house built in Ireland by the noted English architect, John Nash.
Split into simpler sentences: Shanbally Castle was built for Cornelius O'Callaghan, the first Viscount Lismore, in around 1810. It was the largest house built in Ireland by the noted English architect John Nash.