The Guoliang Tunnel was hand carved along the side of, and through, a mountain in China to link the village of Guoliang to the outside area. Some of it, 3/4s of a mile, was carved by just 13 villagers with no power tools, over the course of 5 years

This mountain road has been carved into stone by the local villagers about 40 years ago. They were simply fed up with having to climb steep and dangerous stairs and bamboo ladders to reach their homes. So, in 1972 thirteen villagers decided to start building this man-made wonder.

The village they live in is about 1000 years old

Villagers worked for 15 years (while the major tunnel road only took 5 years), digging the roads along steep mountainside cliffs, carving tunnels and disposing the material through huge window-like openings.

It took at least 4,000 hammers, 12 tons of drill rods... and quite a lot of chisels

In shortage of money, the villagers sold sheep they raised and Chinese yam they planted to buy steel hammers and chisels. And with the help of those simple tools, they managed to make a tunnel road out of mountains by manpower which was opened to traffic at May, 1, 1977. The Guoliang tunnel road is about 1300 meters long, 5 meters high, and 4 meters wide, which is of great significance to the villagers, and gives much convenience to villagers’ planting, economic business, social activities and other activities.

In the past couple of decades, a few machines were brought in to make the tunnel a bit flatter and less bumpy, so vehicles can drive along it easier

https://www.atlasobscura.com/places/guoliang-tunnel
http://www.cookiesound.com/2014/08/breathtaking-views-breathtaking-walks-guoliang-tunnel-road/
https://www.dailymail.co.uk/travel/travel_news/article-2814653/4-000-hammers-12-tons-steel-quite-lot-chisels-one-dangerous-tunnels-world-carved-just-13-villagers-remote-China.html
https://www.topchinatravel.com/china-attractions/guoliang-village.htm