Ballinskelligs Castle, Medieval fortress on Ballinskelligs Bay, County Kerry, Ireland.

Ballinskelligs Castle is a ruined tower house on a narrow, eroding rocky promontory at the south end of Ballinskelligs Bay. Its slightly rectangular plan measures about 10 by 7.85 metres, with ground-floor walls roughly 2 metres thick, and it originally had no more than three storeys. The entrance is on the south-east side, and beam holes on the seaward face suggest an external walkway or stair.

The castle was built in the 16th century by the McCarthy Mór family to protect the bay from pirates and collect fees from merchant ships passing through the waters. Its construction was part of a broader effort by local rulers to maintain control over maritime trade in the region.

The castle is also known as McCarthy Mór Castle, and its Irish name is Caisleán Bhaile an Sceilg. The Irish National Monuments Service's Historic Environment Viewer considers it possibly the same fortified house recorded for the Sigerson clan in the early 17th century. About 300 m south, on another small rocky point, stand the ruins of the early 12th-century St Michael's monastery of Ballinskelligs.

The castle ruins are accessible via a marked path starting from Ballinskelligs Beach, with parking available near the site. The ground can become muddy during wet weather, so sturdy footwear and weather-appropriate clothing are recommended.

Excavations in 1988, after winter storms damaged the ruin, and again in 1991 by John Sheehan's South West Kerry Archaeological Survey found traces of an enclosing wall. They showed the foundations rest directly on rock rather than being sunk into it, with no earlier building beneath and no finds older than the modern period.