Is eighteen bends in mountain road an idiom?

Eighteen bends in a mountain road is not an idiom, it refers to the winding road on the mountain, and eighteen is an imaginary number, representing many bends.

The mountain road means eighteen bends, which means that people living in mountainous areas pass through tortuous roads every day, so there is a saying that the mountain road is tortuous, with nine bends and eighteen bends.

A beautiful sentence describing the eighteen bends of the mountain road;

1. The path follows the valley, passes through the pine forest, and twists and turns like a light-colored belt, winding around the emerald-like mountains.

2. The criss-crossing traffic facilities constitute the blood and bones of the city, which pushes Yangcheng forward to a modern international city.

The ticking road, like a glittering ribbon, floats forward gently in the shade of early summer.

The mountain road is as narrow as a narrow intestine, winding and full of fallen leaves. From time to time, it encounters overflowing mountain springs and its feet are slippery.