Experts are exploring and restoring the Forbidden City's best-preserved, yet least-understood, structure - Emperor Qianlong's long-sealed retirement lodge.

Juanqinzhai is considered the Forbidden City's most exquisite and mysterious structure. And, because it was sealed off for much of a century, it remains one of the compound's best-preserved - yet least-understood - buildings.

Juanqinzhai, which translates as the "Studio of Exhaustion from Diligent Service", was built as the retirement lodge of Qing Dynasty (1644-1911) Emperor Qianlong (1711-99) - who never actually retired. Still, he was the only emperor to, upon ascending to the throne, set a time limit before he would step down, so he wouldn't exceed the 61-year rule of his grandfather, Kangxi. While he technically abdicated in the 60th year of his reign, he continued to wield power until his death.

Related Stories:   Perfection Is Part of the Process   Zooming In on A Place of Mystery

"Qianlong was passionate about art and obsessed with southern China," says Wang Shiwei, deputy director and senior engineer of the Palace Museum's historical architecture department. "He had many dreams he wanted to realize. These are reflected in the styles, arrangements and decorations of the Qianlong Garden (around Juanqinzhai)." But while Qianlong never lived in the lodge built for him, he went there a lot for leisure, so did later emperors, until the Qing's - and China's - last ruler Aisin-Gioro Puyi (1906-67) was expelled from the Palace in 1924.

Juanqinzhai was sealed up ever since.

"Because it was closed off for so long, it remains the least-damaged and least-changed part of the Forbidden City," Wang explains.

"But the lodge was still in need of repair after 200 years. It was time to wake it up."

The Palace Museum signed a $3 million agreement with the World Monuments Fund (WMF) in 2003 to complete the repairs.

Palace Museum curator Shan Jixiang says it's the Palace Museum's first large-scale interior design restoration and its first major international partnership. WMF China representative Liu Chang says the project is also the foundation's largest.

Shan says: "Juanqinzhai stands out among the Forbidden City's 8,704 rooms for its luxurious and personalized style, which shows the pinnacle of Chinese interior design and Qianlong's inner world."