Final answer:
Versailles is a national treasure mainly because of King Louis XIV, who transformed it into a grand palace with extensive gardens in the French Baroque style, featuring the famous Hall of Mirrors.
Step-by-step explanation:
The major reason that Versailles exists as the national treasure it is today is primarily due to the efforts of King Louis XIV. While King Louis XIII initially purchased the land and built a hunting lodge on the site, it was his son, Louis XIV, who envisioned and executed the grand transformation of Versailles into the sprawling palace with its elaborate gardens, which are known today. During his reign, Louis XIV initiated and oversaw four major building campaigns to create the palace and its gardens in the extravagant French Baroque style. The palace's grandeur, including the notable Hall of Mirrors and the extensive formal gardens which typify the jardina la francaise, were meticulously designed to reflect the absolute power and glory of the Sun King.