Visitors can stand in the dry bed of the old moat, traverse imaginative gangways over the encroaching river (the Poddle, not the Liffey), and view the stairs where boats once brought provisions to the castle.
The moat was used for self defense only and served no other purpose. 
mnli hypothesis: The moat was used for self defense only and served no other purpose.  premise: Visitors can stand in the dry bed of the old moat, traverse imaginative gangways over the encroaching river (the Poddle, not the Liffey), and view the stairs where boats once brought provisions to the castle.