13.2 million euro was spent on 46 sites.
There are about 700 national monuments in the care of the Office of Public Works across the country.
But less than 50 operate with a guide service, some of which are closed or are free.
Details released under the Freedom of Information Act show it cost 13.2 million euro to staff and maintain these sites in 2019.
The income from these national monuments was less than 6.3 million euro.
Kilmainham Goal operated at a profit of nearly 800,000 euro, with more than 2 million euro taken in in admissions last year.
The Rock of Cashel made a profit of nearly half a million euro, with over 1.5 million euro taken in.
But several other sites operated at significant losses.
The OPW says it charges admissions to certain heritage visitor sites in its care, but doesn't have a very commercial pricing strategy.
It says these sites are mainly a public cultural asset.