Two more St. Patrick's Day cards, the one on the right from 1911, the one on the left undated.
Both show the Old Weir Bridge in Killarney, Ireland. Killarney, County Kerry, is one of the most well-loved tourist destinations in Ireland and there are boat rides available that pass under the Old Weir Bridge, except when the waters are low when you have to get out of the boat and walk around the bridge to the other side.
Check out the multiplicity of Irish icons on the card on the right: the pipe, the harp, and shamrock. A good site for information on these Irish symbols and more can be found here (you have to scroll down a bit to find the "Irish Symbols" listing). More information than you ever knew existed about the legend of the shamrock can be found here.