Photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)

Aerial photo taken on May 25, 2019 shows the 326-meter-high Bailong Elevator, the world's highest outdoor elevator, shrouded by fog at the Wulingyuan Scenic Area in Zhangjiajie, central China's Hunan Province. (Xinhua/Wu Yongbing)