Castleguard Cave is the longest cave system currently known in Canada (21km) and the foremost example anywhere of a cavern extending underneath a modern glacier. It displays many striking features of interactions between glaciers and karst aquifers, a complex modern climate, rich mineralization, and a troglobitic fauna that has possibly survived one or more ice ages beneath deep ice cover in the heart of the Rocky Mountains.KeywordsCanada; glaciers; alpine karst; alpine caves