Electric Parks were an Amusement phenomenon prior to WW I.  This Real Photo Postcard (RPPC) shows the bridge at Electric Park in Niverville, NY (Columbia Co.) on Kinderhook Lake.  The Park was fed by the Albany and Hudson Railroad.  The receiving Postmark is Leyden, Mass.  A Discontinued Post Office (DPO) that was in business from 1828 to 1935.  The stamp is #328.  The lot includes the Postcard and a three-page reprint from Wiki.