McCarthy’s castle is located to the north of the Abbey sitting on the tip of a narrow promontory of land that juts into the sea. This tower house is probably 16th century in date and associated with the McCarthy’s who were chieftains in Cork and Kerry. The promontory suffers badly from erosion and has changed substantially in living memory, some of this change is often attributed to the 20th century construction of the concrete pier that lies at the end of the Promontory. The castle ruins remain largely intact; however, the southern corner is badly damaged with a breakthrough in the wall in this area. This is partly due to exposure to the sea and the wall being thinner due to the mural stairs located in this corner of the tower house. The land around the castle is impacted by erosion. Excavations were undertaken at the castle in 1988 and 1991 by John Sheehan, University College Cork. Two external lean-to structures with pitched-cobble floors identified during excavation and post-dating the primary period of occupation of the castle are believed to have been a fish curling station. It is recorded that Sir William Petty established a fishery at Ballinskelligs.
The dated tree stump from Inny strand tells how a Bronze Age forest was present in the north of the bay, the continuation of buried peats past the present low water mark indicate the forest covered the area that denotes the intertidal zone today. The basal dates of the peat cores around the Bay inform of the formation dates and phases of the wetlands that now encompass Ballinskelligs Bay. These peat cores will provide further insights into the environmental and climate records for the Bay since the Neolithic Period. The palaeo-environmental evidence when considered in context of the pattern of change recorded due to geological processes around the bay since at least the mid-18th century and in context of predicted climate change impacts due to atmospheric change such as rising sea level indicates a continual loss of the coastal margin into the future as the predominate forces at play continue to enlarge the bay here at Ballinskelligs.