In some of his shots, such details as the eaves of the halls, the shadows cast by trees, the bridges and the lights, are highlighted to capture the beauty that tourists often overlook.

Li believes getting the perfect angle and perspective usually requires great patience. The sense of history can easily be lost in the flood of visitors when the Palace Museum is open.

While it only takes a split second to click the shutter, he has to spend hours planning, traveling and finding the best vantage point.

Sometimes, a good picture requires luck. Li remembers accidentally taking one photo of flowers growing on the palace walls. The scene made him think of the tragic lives of the concubines behind the walls.

"Photos are my visual language to reveal background stories in an aesthetic and artistic way," Li says.

"The empty halls, the quiet courtyards, the doors and windows with fading paint, and the long grass in the corners of the squares evoke a strong sense of history."

Li has captured moments in which the Forbidden City's appearance changes with the weather, lighting and seasons.

He has published several photo albums and staged exhibitions at home and abroad.

Li says his exploration of the world's largest surviving palatial architecture complex, covering 720,000 square meters, won't stop, and he will continue to record the six centuries of history behind the buildings.

Those seeking to follow in the footsteps of Li and other photographers to first aim their cameras at the Palace Museum have encountered difficulty finding original takes.