The "green giant" is ready to serve and whisk passengers and cargo between China and Laos soon. The thousand-plus-kilometer link stretches from the southwestern Chinese city of Kunming to the Laotian capital of Vientiane.

YANG JINGHAO Yunnan Province "The cross-border rail line is one of the major projects in China's proposed Belt and Road Initiative. It's also part of Laos's strategy to go from a landlocked country to a land-linked hub."

Builders say the railway's construction has been a tough nut to crack. Within China, over 87 percent of the line are tunnels and bridges due to the mountains and rivers along its way. They say this grand bridge is an iconic project. The highest pier is over 150 meters tall, equal to a 54-storey building. And the perils some workers have faced are beyond the imagination of many.

Zhou Kunpeng describes his tunnel-building experience as a battle against emergencies – landslides, floods and mud bursts.

ZHOU KUNPENG China Railway Tunnel Group Company "Another challenge was the temperature, which could reach as high as 52 degrees Celsius in the tunnel. We would be soaked in sweat after staying inside for 10 minutes. We used ice to cool down and tried to improve ventilation, but some of the workers would still faint."

He says the mission has been a test of both technology and will power.

ZHOU KUNPENG China Railway Tunnel Group Company "It takes just six minutes to pass through this tunnel, but we spent five years building it. And during that period, we've laughed and cried. We were in despair sometimes, but still determined."

Environmental protection has also been central to construction efforts.

XU TAO Chief Designer of Chinese Section, China-Laos Railway "The region is abundant with wild animals and plants. There are also many environmentally sensitive areas. So, we conducted a thorough survey to know the scope of nature reserves and ways to bypass them."

The designer says minimal impact was in mind every step of the way.

XU TAO Chief Designer of Chinese Section, China-Laos Railway "We didn't set up piers on the rivers or at the banks to avoid pollution. During construction, we also adopted techniques to prevent debris from falling into rivers so as not to harm marine life."

Energy conservation will also be a highlight once the railway comes into use. Authorities say all stations along the line have been equipped with energy-saving devices. Its builders say the project has not just been a symbol of friendship between two nations, but also a symbol of harmony between humans and nature. Yang Jinghao, CGTN, Yunnan Province.