Parking at indicated entrance, follow the paved road to the lower reservoir, turning left (East) along the top of the dam towards the hillside straight ahead. Take a moment to enjoy the views of the reservoir, framed by the Dublin mountains, and the glorious silence.
At the end of the wall, you will be faced with a steep hillside covered with trees. Going up and down this hill will be the most trickest parts of this cache so either you will be scrambling on all fours or get a good set of sticks to help you. Either way, take care. Speaking of the trees, enjoy the variety that have been planted here.
Head up the hill, veering left (North). As mentioned, it is very steep. Try heading to the top as much as possible rather than going straight across, as it levels out and it turns into a pleasant walk, with many sheep paths you can follow. Parts of the hillside have collapsed as landslides, so there are steep drops in places. They are easily seen however, but be mindful and stick to the paths and you'll be fine. Do not attempt in the dark! Attached are some pictures of the path I took as well as the cache location. Also, do not get fooled by the apparent promixity to the dam, it can get disorientating walking through the forest, and although you won't end up lost for hours or anything like that, it is annoying to retrace your steps, so recording your route on a GPS is a good idea.
The geocache itself is very well hidden under the roots of a fallen tree. That's not a spoiler once you see the number of fallen trees :-P After signing the geocache, make sure to cover it up again, and simply retrace your steps, being mindful of the landslide drops, and the steep ending to this geocache. Enjoy :-)