Some apartments were built on the site of what was probably a nice period house around 30 years ago, and this little triangle of land nearest the road junction was leftover, for whatever reason the developer did not use it.
Sure, undisturbed back gardens can be very good havens for city wildlife, and for that reason it is a good thing. But don't get the idea that it is worth a visit.
There are countless other (better for wildlife) long private back gardens around Ranelagh and Rathmines.
But hey, there is a very interesting old milestone on the far side of the road "Rathmines 1847" Its from the days when Rathmines was its own little town, with Dublin to the north and the fields of Donnybrook to the south. Donnybrook Fair was an infamous annual horsefair, piss-up and general brawl that people used to come from far and wide to enjoy.