Complex sentence: The ceilings were ornamented plaster set in a square pattern by the old caretaker (who lived in a small house on the Elizabeth St end) after hours who was a never-ending source of school and local area history.
Split into simpler sentences: The ceilings were ornamented plaster set in a square pattern by the old caretaker (who lived in a small house on the Elizabeth St end) after hours. He was a never-ending source of school and local area history.