Bock Casemates

The Bock is the rocky promontory where Count Siegfried built his first castle in 963 — the founding act of Luxembourg as a polity. The casemates carved into and beneath it are the city's most-visited sight. The tunnels are dark, damp, and unfussily lit; you climb stairs cut into the rock, peer through cannon ports at the Alzette valley far below, and emerge through the dramatic Bock cliff face.

The casemates run for 17 of their original 23 kilometres and are a UNESCO listing in their own right. Open daily March to October, with shorter hours in the shoulder months. Allow at least an hour; wear shoes with grip and bring a layer — even in summer it is cold below ground.

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A story
The Spanish began tunnelling into the Bock cliff in 1644; the Austrians extended the network to 23 kilometres in the 18th century. When the great fortress was dismantled in 1867 the casemates were left intact because filling them in would have caused the houses above to collapse. During both World Wars they sheltered the entire civilian population — 35,000 people, with their own bakeries and slaughterhouses underground.