The Green Route is a 3 km loop hike, which is considered to be easy. As compared to the Blue Route, the Green Route is actually more of a walk rather then a hike. There is no elevation. The main reason why we did the Green Route after finishing the Blue Route was that we wanted to see the Monastic City. The Green Route takes you around the Lower Lake.
The Monastic City is one of the most important monastic sites in Ireland. It dates back to the 6th century. If you wish to read more background information on this site, the tourism website of the County Wicklow provides a great overview.