Complex sentence: The Annenberg Retreat at Sunnylands is the former private estate of Mr. and Mrs. Walter H. Annenberg that opened in March 2012 as a high-level retreat center, historic house, and visitor center.
Split into simpler sentences: The Annenberg Retreat at Sunnylands is the former private estate of Mr. and Mrs. Walter H. Annenberg. It opened in March 2012 as a high-level retreat center, historic house, and visitor center.