Complex sentence: He made it his private estate, and from 1906 until the 1930s, du Pont added extensively to the property, the most notable additions being the beautiful conservatory, complete with a massive pipe organ, and an extensive system of fountains.
Split into simpler sentences: He made it his private estate, and from 1906 until the 1930s, du Pont added extensively to the property. Du Pont was add many features to the garden, the most notable additions being the massive conservatory, complete with a massive pipe organ, and an extensive system of fountains.