Complex sentence: After Lord Orkney's death the palaces continued to be the residence of the Bishops of Orkney sporadically until 1688, when they became the property of the Crown, and fell into ruin in the 18th century.
Split into simpler sentences: After Lord Orkney's death the structures continued to be the residence of the Bishops of Orkney sporadically until 1688. It then became the property of the Crown, and fell into ruin in the 18th century.