The fortified bulwarks and the equally steeped in history old town enjoy worldwide renown. In 1994 they were added to the UNESCO list of World Heritage sites. The subterranean fortifications of the casemates on the massive supporting rock, the birthplace of the city of Luxembourg, are all included in the highlights of any visit to Luxembourg.
Today you have a splendid view over the upper and lower town from the arrow slits. From March to October you can view these enormous galleries daily from 10 am to 5 pm. More info here.