I approached this site from the bottom of the cliff in Hollywood glen at N934024. There is a small waterfall on the east side of the road that runs through the glen and just beside this is a pumping house. Directly opposite this you can see a track up towards the cliff-top. It is extremely steep and arduous.
This is called a rath here but I'd say promontory fort would better describe it. It's D-shaped, with the straight line of the D to the east and the maw of the cliff. It's maybe 40 metres north-south, but the ditch, where it can be seen below the vegetation, is impressive. There are some earthfast boulders peeping out of the structure of the defences but it's hard to say what the bank is made from. Allowing for silting over time, I'd say possibly 3 metres in places from bottom of ditch to top of bank.
There are no traces of any structure inside the small area of the fort, which has space for one homestead. Did the people who lived here, if this was a habitation site, build the stone circle below? The views west down to the N81, where traffic blasts noisily by, and across the Kildare plain are great. North-north-east the cairn of Slievecorragh is visible.