I found this Welcome sign while I was on the Trans-Mongolian Railway from Beijing, China to Ulan-Ude, Russia.
"Zhangjiakou, also known also by several other names, is a prefecture-level city in northwestern Hebei province, bordering Beijing to the southeast, Inner Mongolia to the north and west and Shanxi to the southwest. Its administrative area has a population of 4.35 million, and covers 36,947 square kilometres (14,265 sq mi). The urban area of Zhangjiakou is divided into Qiaoxi and Qiaodong Districts which have 473,193 inhabitants in 2010, but the prefecture-level city is much larger, spanning around 36,800 square kilometres (14,200 sq mi). Due to its position on several important transport arteries, it is a critical transport node for travel between Hebei and Inner Mongolia and connecting northwest China, Mongolia, and Beijing."
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Because of its strategic position above and northwest of Beijing, Zhangjiakou has been nicknamed "Beijing's Northern Door".