What castle in Ireland once occupied by the MacDonnells is accessible by a bridge?
Glenarm: Dating back to Norman times, the village is the family seat of the MacDonnells, who once occupied Dunluce Castle on the north coast. Dunluce Castle:  It is located on the edge of a basalt outcropping in County Antrim (between Portballintrae and Portrush), and is accessible via a bridge connecting it to the mainland.
Dunluce Castle