The Office of Public Works (OPW) is waiving admission fees to a number of historic sites in an effort to attract more interest in them.
The decision to give free entry is also an attempt to try to divert numbers away from the country's most popular sites, which are at or near saturation point.
Preliminary figures for visitor numbers in 2004 show that the four most popular attractions - the Rock of Cashel, Brú na Boinne, Kilkenny Castle and Muckross House and gardens in Killarney - between them attracted 822,000 visitors out of a total visitor number of 2.2 million to some 60 OPW-managed historic sites.
Some 251,615 people visited the Rock of Cashel in Co Tipperary last year, an increase of over 6,000 on the previous year.
Similar increases were recorded for Kilkenny Castle, which was visited by 168,000 people, and Muckross House, which saw over 180,000 visitors,with thousands more visiting its folk farms and gardens.
Numbers to the Brú na Boinne/ Newgrange site were down slightly, at 213,674. However, this site is thought to have reached saturation point.
Kilmainham Gaol in Dublin had over 168,000 people touring the gaol last year, an increase of over 13,000 on the previous year. Kilmainham and the Rock of Cashel are also thought to be at saturation point.
However, other centres such as the Blasket Centre in Kerry and Garnish Island in west Cork showed a drop in numbers. Numbers for Garnish dropped from 69,493 in 2003 to 67,359 last year.
Among the sites earmarked for free entry are St Audoen's Church in Dublin, the only remaining medieval parish church in Dublin and sited in the heart of the walled medieval city.
Also free this year is Dungarvan Castle, which attracted just 7,000 people last years.
Ferns Castle and Ballyhack Castle, built by the Knights Hospitallers of St John during the Crusades in Co Wexford, are free, along with Maynooth Castle and the Desmond Hall in Limerick.
The Corlea trackway and visitor centre in Longford, which contains the largest oak road uncovered in Europe, is also free. Last year the centre received only 3,021 visitors.
OPW spokesman George Moir said the decision to drop charges was part of "a wider experiment", and an attempt to stimulate more interest among local populations in the various sites.