The caves, casemates and Fort Sint Pieter
The Sint-Pietersberg hides hundreds of kilometres of man-made galleries cut for marl, later used as shelters and escape routes, with the 18th-century Fort Sint Pieter above them. Tours run daily from Luikerweg and last about an hour.
Guided tour only - there is no independent access. Book ahead, and note it is not wheelchair accessible.
Official site