Driving down the M18 somewhere past Shannon, I saw something. Using Google Maps, I retraced my course and found it is the Belvedere Folly, the Gazebo at Dromoland Castle.
“Probably the finest of all the Irish gazebos is the one at Dromoland Castle, Newmarket-on-Fergus, Co. Clare. It survives from a formal baroque garden of the early eighteenth century, which was subsequently overlaid by a more natural landscape later in the same century. The early garden and its ornamental buildings were commissioned by Sir Edward O’Brien. The drawings for it, including a fine plan of the layout, mentioned earlier, have survived. The gazebo stands some distance from the house, which is now a hotel, on top of an artificial mound on a flat hill commanding extensive views, and would have been well suited for its intended purpose of watching horse-racing. “
The Follies and Garden Buildings of Ireland, James Howley
Sir Edward O’Brien, 2nd Baronet commissioned architect John Aheron to design the Gazebo around 1740. It is situated on Turret Hill, across the road from the main entrance gateway.
It was likely built as a vantage for observing the training of horses. That makes it a belvedere, a raised structure from which to view.