Blackstairs Mountain, Mountain summit in County Carlow and Wexford, Ireland

Blackstairs Mountain, called An Staighre Dubh in Irish, is the second-highest summit of the Blackstairs Mountains in southern Leinster, reaching 735 metres. The mountain stretches from Rathgeran to Gowlin at Cathaoirs Den, forming a long ridge above County Carlow and County Wexford.

The mountain range formed through geological processes over millions of years, shaping the modern landscape of southeastern Ireland. A cave on the southwestern ridge connects to a local story from the 18th century involving a figure from Irish history.

The Irish name An Staighre Dubh means "the black stairs", after the stepped, dark-looking slope of the peak. Each year the mountain hosts a Lughnasa gathering known locally as Mountain Sunday, when people climb to the summit for the harvest festival held on the last Sunday of July.

Hiking typically starts at Scullogue Gap, where marked trails offer a gradual climb taking around two hours to reach the summit. The path is well-worn on this route and manageable for different fitness levels, though proper footwear and weather protection are recommended.

The mountain runs from Rathgeran to Gowlin at Cathaoirs Den, a spot on the southwestern ridge whose name is often anglicised as Caher Roe's Den. The summit is also an assembly site for the feast of Lughnasa, held here as Mountain Sunday.