Doors open on a hidden corner of Forbidden City

When restorers opened the door on the Qianlong Emperor's favourite studio in the Forbidden City, dust three inches thick on the exquisitely carved surfaces bore testament to decades of abandonment. "It felt like the last emperor had just turned the key in the door and left," was the verdict of one expert.

Yesterday, after a multimillion-dollar effort, Juanqinzhai, the "Studio of Exhaustion from Diligent Service", was revealed in all its dazzling glory. It is the first time the Chinese have collaborated with Western experts on such an elaborate interior project, with the work carried out by the Palace Museum in Beijing and the World Monuments Fund.

The studio was built in the late 18th century as part of a bigger retirement retreat by the Qianlong Emperor. He died in 1795 before the building was completed but Juanqinzhai was finished exactly as he wanted – a mini-palace within a palace, including a private theatre, with seating for one (a throne, naturally). Double-sided embroidery was all the rage in those days, and there was plenty of that. And only the best materials would do for the carved inner bamboo marquetry and white jade cartouches that decorate the Reception Hall.

The modern-day restoration team has tried to stay true to the emperor's original vision. One undoubted highlight is the mural adorning the theatre roof – a silk trompe l'oeil painting of a bamboo trellis groaning with wisteria vines in full bloom, and dotted with flitting magpies. The mural was conceived under the guidance of a Jesuit painter, Giuseppe Castiglione, and points to the emperor's fascination with the latest European artistic ideas of perspective. It was designed to give the appearance of light and airiness, in contrast to the oppressive cold of a Beijing winter. Restoring the artwork was a tricky job, involving a revolutionary technique of stripping the paper from behind.

The building had been shuttered by the last Emperor, Pu Yi, in the early 1920s and it lay abandoned until 1999. "A woodworker came in and picked up all the pieces of jade and wood which had fallen down and had 35,000 plastic bags," recalled Nancy Berliner, curator of Chinese Art at the Peabody Essex Museum in Salem.

The communists have long been ambiguous about this network of temples. Chairman Mao Zedong would have happily done away with the Forbidden City to make way for a motorway if he had had the money, and it took the personal intervention of Premier Zhou Enlai to stop Red Guards tearing it down during the Cultural Revolution.