Aran Islands

 "On the cliff tops, ancient forts such as Dún Aengus on Inishmór and Dún Chonchúir on Inishmaan are some of the oldest archaeological remains in Ireland. A lacework of ancient stone walls enfolds all three islands to contain local livestock. Also found are early clocháns (dry-stone beehive huts from the early-Christian period). Enda of Aran founded the first true Irish Monastery near Killeany (Cill Éinne or Church of Enda). In time there were a dozen monasteries on Inishmór alone. Many Irish saints had some connection with Aran: St. Brendan was blessed for his voyage there; Jarlath of Tuam, Finnian of Clonard, and St. Columba called it the "Sun of the West."" From  http://en.wikipedia.org/wiki/Aran_Islands

A lacework

Dún Chonchúir on Inishmaan

Megalithic Ireland

Map of Ireland, showing the Counties and historical Provinces
http://www.irishmegaliths.org.uk/iremap.htm
For each county, there is the list of places and images. See for instance:
http://www.irishmegaliths.org.uk/galway.htm