Introduction to Luxembourg City: The entire city of Luxembourg City was built along the hills on both sides of the river valley. The ancient city was repeatedly invaded by foreign invaders after the 15th century. It was ruled by Spain, France, Austria and other countries for more than 400 years, and was destroyed for more than 20 years. Second-rate. During this period, the brave people of Luxembourg City built many strong castles to resist foreign invasion. These castles are of first-class architecture and have high ornamental value. They are listed as one of the "World Cultural Heritage" by UNESCO. After Luxembourg was recognized as a neutral country in 1883, some castles were demolished. Later, a large number of castles were converted into parks, leaving only some stone walls as permanent memorials.