The centre of Luxembourg is located very beautifully - on a rock isolated from three sides by deep gorges, where two small rivers flow.
The city received its town charter in 1244. Because of its strategic position it was very strongly fortified, and very often passed from hand to hand. In 1684 the city was captured by the French, who then surrounded it with a modern system of fortifications designed by one of the best builders of fortresses of all time - Sebastian Vauban.
At the end of the Palatinate Warvin 1697 the city returned in Spanish hands, and after the War of the Spanish Succession it passed into the hands of Austria. During the French Revolution the city was occupied by France twice - briefly in 1793 and again after 7 months of siege, after which the French engineer Lazare Carnot stated that Luxembourg is the best fortress in the world except Gibraltar, and thus came the city started to be called "Gibraltar of the North" (per Wikipedia).
Today you can visit the remains of a fortress for hours, or half an hour on foot or sitting in a tourist bus or train. The mininum you should do is enjoying the mountain views in the very center, then going dowin in the elevator (located at the Palace of Justice) to the Grund district to look at the city from below.
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