23-kilometre-long galleries were enlarged forty years later by Vauban, the French military engineer and fortress builder, and in the 18th century by the Austrians. The subterranean defensive passages were placed on different levels and reached down as far as 40 metres. It is these impressive defense works that caused Luxembourg to get the name "Gibraltar of the North." After the dismantling of the fortress in 1867, 17 kilometres of the casemates were spared and left in good condition. This tourist attraction in luxembourg has been open to the public since 1933 and provides good opportunity to glance at the history of the country.