This is the vent hole which was first discovered long ago. The Victorian fascination with warm mineral waters and good health drove the development of early Banff. Bathhouses beside the basin spring were framed in a rustic crossed log motif that was to become Banff's signature style of architecture. A tunnel was blasted up the Cave outlet spring to allow easier access and the Basin spring was enlarged to about three times its original size. By 1916, the largest swimming pool in Canada was in full use, though few Canadians know that its construction was completed by labourers interned at the Cave and Basin during the First World War.