sets of four):
Portals –

Dun Aengus Stone Fort
Killevy Church Ruin
St. Kevin's Monastery II
Trinity Church Ruin
Dolmens –
Poulnabrone Dolmen
Dolmen on Inishmore
Haroldstown Dolmen
Dolmen at Kilclooney More
Standing Stones and Crosses –
Carrowmore North Monastic Cross
Carrowmore South Monastic Cross
Eightercua Stones
Piper Stones I
Piper Stones II
Stones of Newgrange