If you travel light equiped for youth hostel you can walk easily in one day and a half form Dublin to Glendalough. From marlay park in dublin to the first youth hostel is half a day hike. from there to Glendalough is a fulls day hike and a rather big one but doable. The path is not to bad when there is no snow. a little rain isn't a big problem for this route
There are some routes in the wicklow mountains but it ain't much besides the Wicklow Way.
There is something like St. kevins route or way from glendalough to hollywood or Valleymount an chrois (variant). Not really spectaculair route IMHO
The route I mentioned is the first or last part of the wicklow way. I did this part in two half days and a day (total 2 days with a tent and food and such) without bagage you might be able to do the same in 1 and half a day. it's a nice hike with the possibility to climb the highest peak Djouce mountain, the powerscourt waterfall, nice paths over the bogs on a boardwalk and such, some very nice views. In and out is easy From dublin public transport to Marlay park Dublin and from glendalough St. Kevins bus back into the heart of Dublin
