It gives detailed explanations for many ancient sites around Ireland, including in the case of Monasterboice, identifying which Bible stories are depicted on the high crosses. Now, the one complication to this website is that I can't find a way to give you a direct link to the specific page for a place we visited. What I will do is tell you where to click on the left-hand column to bring up the correct page.
I will list the sites we visited, in the order of our itinerary. Here again is the link. Enjoy!
For Knowth Passage Tombs, from the home page click County MEATH, then KNOWTH.
For Monasterboice, click County LOUTH, then MONASTERBOICE, then HIGH CROSSES.
For Corcomroe Abbey, click County CLARE, then CORCOMROE ABBEY.
Also in County Clare is Poulnabrone Portal Tomb.
For Blarney Castle, Click on County CORK, then BLARNEY.
For Butler Castle, Click on County KILKENNY, then KILKENNY CITY, then THE CASTLE.
For Glendalough, Click on County WICKLOW, then GLENDALOUGH, then MONASTIC SITE.
For St. Brigid's Cathedral, Click on County KILDARE, then KILDARE, then CATHEDRAL (and FIRE TEMPLE and ROUND TOWER)