Aaaah, holed-stone portals!! My favourite! Isn't it amazing that these beautifully gorgeous veils between the seen and the unseen are found almost everywhere in surprisingly equal creations?
Check the ones in Malta, Iberia, France, Denmark, etc
I'll contact you in a coupla weeks so's to get precise details of the ones you are coming across in Eire. Tho' I suppose they'll be in your site soon.