If they are national monuments and have a proper sign-board then access should be free.

Unfortunately, when some of the National Monuments were pruchased by the state a right of way was not always purchased (D'OH!). This is the problem with Carnbane West at Loughcrew. The landowner says no right of way was included in the purchase. Duchas* say different. Stalemate, because Duchas won't go to court for it.

The best bet is to check at the local council offices to see if rights of way exist. If they do then you can not be charged ... but you must stick to the path (obviously).

If there isn't a right of way then they can charge you for access.

* I know they ain't called that now, but it's easier to write Duchas :-)