(CNN) — Beijing's Forbidden City is one of the Chinese capital's must-see tourist attractions, a UNESCO World Heritage site which provides incredible insight into the lives of China's emperors.

But come 2020, there'll be a new reason to visit this former imperial palace when the complex's Qianlong Garden will be open to the public for the first time.

The Qianlong Garden spans two acres of the Forbidden City and was built by its namesake Emperor Qianlong, the fourth emperor of the Qing Dynasty, in the 1770s.

In 2004, 80 years after the last emperor left, the World Monuments Fund -- a non-profit organization that preserves historic and cultural sites worldwide -- and China's Palace Museum partnered up on a large-scale preservation project for the Qianlong Garden.

Inside closed doors

The Qianlong Garden in Beijing's Forbidden City has been renovated and will be open to the public in 2020. Courtesy World Monuments Fund

Qianlong, who ruled from 1736-1795, conceived the area to be part of his retirement complex, complete with four courtyards, pavilions, intricate rockery gardens and stunning interiors.

The interiors of the Qianlong Garden include striking design details such as bamboo marquetry and trompe l'oeil paintings -- a more European art format.

They were preserved thanks to an unusual edict from Qianlong, which banned future sovereigns from altering the complex.

Inside the restored Fuwangge (Belvedere of Viewing Achievements). Courtesy World Monuments Fund

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Still, after decades of neglect, much work is now being done to transform the Garden back to its former glory.

Progress has been made -- Juanqinzhai (Studio of Exhaustion from Diligent Service) was completed in 2008, while conservation of three other structures in the fourth courtyard, including Fuwangge (Belvedere of Viewing Achievements), Zhuxiangguan (Lodge of Bamboo Fragrance) and Yucuixuan (Bower of Purest Jade) was completed in 2016.

Juanqinzhai -- which was intended as a relaxation space -- includes a private theater and receiving room. These striking interiors are embellished with bamboo skin carvings, jade inlays and intricate textile decorations.

The World Monuments Fund says that restoration of buildings in the first, second, and third courtyards is currently underway and slated to be finished in 2020, just in time for the 600th anniversary of the Forbidden City.

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New Interpretation Center

The complex is due to reopen in 2020. Pictured here: Juanqinzhai (Studio of Exhaustion from Diligent Service). Courtesy World Monuments Fund

The Fund also announced that American architect Annabelle Selldorf -- of Selldorf Architects -- will design a new Qianlong Garden Interpretation Center within the Forbidden City.