"We migrate every year. We leave the Zhengyangmen Gate in July and return in April," says the swift in the documentary.

According to Guan Zhanxiu, director of Beijing Central Axis heritage protection center, the swifts' migratory route is particularly long. "They fly out of our country through the Xinjiang Uygur autonomous region, then through several Central Asian countries and along the Red Sea before finally ending up in South Africa. It is almost similar to our ancient Silk Road," Guan says.

In 2018, Guan's team set up 12 cameras around an actual swift's nest to observe and protect the birds within, and even witnessed a couple of swift families breeding.

Produced by the information office of the Beijing municipal government and Beijing Radio and Television Station, the bilingual 30-episode series takes the audience on a journey exploring Beijing, presenting the capital city in a down-to-earth and authentic way, showing the richness and development of the city.