Glendalough (glĕn`dəlō'), wooded valley, Co. Wicklow, E Republic of Ireland, W of Wicklow. It is noted for the ruins of several churches of the 11th and 12th cent. (part of the center of Irish Christianity that St. Kevin founded). Also of interest are a round tower and Kevin's Cross (a granite monolith). A ledge in the face of the rocky mountainside, above the lake that lies at the foot of the vale, is the legendary retreat of St. Kevin.