Glendalough is a tiny village in Co. Wicklow, Ireland. No major road arrives here, but it is a rather popular hiking day trip destination from Dublin. Bus connections with Dublin tend to be atrocious, with connecting buses up to 1.30h apart in Ashford. That is of course, if you are not going with an organized trip with their own bus.
This is where buses to and from Dublin stop in the area. From the Asford Community and Heritage Centre heading south turn right into the R764 road. After 100 yards on the left there is an entrance to a cul-de-sac, River Walk, with a bit of shoulder and space to stop. A better spot is a further 150 yards where the road R763 detaches from road R764. Waiting times are less than an hour (which is still better than the bus connections).
This tends to be harder than getting in as there is a smaller chance to find locals. The best spots tend to be the Visitor Centre Car Park and the Weavers Kitchen Pub, about 1km east of the village.
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There is a good chance that near-empty local buses will stop even outside official bus stops to pick you up. The ticket can be purchased onboard. Whether you consider that hitchhiking it is up to you.