The only military construction in the world that depends on goats.
The Simatai section of the Great Wall is 120km north-east of Beijing, runs along the tops of high peaks and cliff edges, and is almost bereft of tourists.
The problems caused by this mountainous construction sight were alleviated somewhat by the presence of the local mountain goats. They served as transporters, carrying bricks up the steep, rocky slopes. The goats became a popular source of income for the locals and their numbers rose rapidly. However, they later became a liability when they began to eat the surrounding vegetation that protected the soil around the Wall from erosion. So, the locals were finally banned from raising them.
Being less populated by tourists, this section hasn’t been restored to perfection. This, while adding to its charm, means you have to look where you’re treading every now and again so as not to roll down the hillside to horrible death.
(It also means that you can fire a few sneaky, imaginary arrows at the advancing Mongol hordes without anyone seeing).