There are good facilities available at this parkrun. There is a car park close to the start line, though it is small, but there is a large car park about a five minute walk further away. There is a Dublin bus route to the park, which I found surprising given the rural location. There are also toilets available onsite.
The grounds of Ardgillan castle are very pretty, with some well maintained flower beds and gardens close to the main house, and further away from the house are some nice green areas and woodlands. The run passes by all of these and starts and finishes at the main house. The run surface is mostly packed gravel but there are some areas with large loose chipping stones, which present a slight trip hazard. There are permanent distance and direction markers along the route which are quite useful. There is a fair bit of climbing on this run so this is not a run for a PB attempt, but it is this hill that adds a little interest to the run; after two laps at the bottom of the park, the last 200 metres or so consists of a tough climb up to the finish line at the main house. This is a real test at the end of the run.
There is a coffee shop in the main house. The coffee was nice and there were some very interesting maps on the wall of a survey of Dublin that was was done in 1916. The café opens up to a garden at the back of the house which would be nice on a sunny day, but it was a little wet when I was there. Interestingly, there is also another cafe a few minutes away which is a dog friendly cafe, which is a good option if you brought along your dog for the run.
One of the things that is really striking about this parkrun is the view. The grounds of Ardgillan castle are on an elevated site right next to the coast, so there is a nice view out east to the Irish Sea. I can imagine on a sunny morning that this would look quite spectacular with the rising sun. The grounds themselves are well maintained, and I think this would be a great place to go in the middle of summer with all the flowers in bloom. I was impressed also by the amount of people that cycled to this parkrun, rather than drive. Also, there was a good community aspect to this event, with a big crowd gathering for the post run coffee.