The English name Glendalough comes from the Irish Gleann Dá Locha which translates to "The valley of the two lakes".St. Kevin founded a monastery here in the sixth century which continued to expand for 600 years, but was destroyed in 1398. The buildings which survive date from the 8th and 12th centuries. The most famous is the round tower which is 34m high and 16m in circumference at the base. A cathedral, stone churches and decorated crosses also survived. http://wikitravel.org/en/Glendalough