The Casino in Marino has underground tunnels too.
These links give some background, and one describes a ½ mile tunnel. The tunnel was useful for cold storage, according to one piece.
http://www.iol.ie/~stdavids/Other_Interesting_Features.html#other
http://www.heritageireland.ie/en/HistoricSites/DublinArea/CasinoMarinoDublin/
I grew up in the area, and there was an urban legend describing a complicated network of several miles of tunnels. One was supposed to extend as far as St David’s in Artane, about a mile away. As I say, probably an urban legend…