This is a really impressive site. I remember reading about it in the Discovery Programmes North Munster Project (I had a loan of it for a few days). I believe it is classified as a Bronze Age Barrow.
I would like to give the exact dims because it is huge and really the pictures don't do it justice.
There are three rings around it as far as I could see. The inner one being about 1.5m high and the ditch in between is filled with water.
What really excited me was the views from it. To the east you have the many notches of the Galtys, south the Ballyhouras but even more importantly to the North you can clearly see the fairy mound of Cnoc Aine.
I think this mound/ barrow may be in some way related to the many monuments in the area.
The word rathanny is meant to come from Rath-eanaighe or the fort of the marsh. However I wonder is there any link to RathAine? With Anny being a corruption of this?
As for how to find it, I parked at the soccer field beside Hospital and walked thru the fields. It is about 1km from the soccer field.
There may be a track thru a farm but you will have to ask for permission etc. Basically you will need a GPS and to be honest I wouldnt fancy going down here in wet weather. I think it would live up to Rath of the marshes!