most of the country's most famous tourist sites have witnessed a dramatic decline in visitor numbers over the past three years.

The number of people making the pilgrimage to Newgrange, Clonmacnoise, Cashel and other most historic destinations has fallen by as much as 20%.

The government has blamed a combination of bad weather, volcanic ash and the general fall-off in international tourism.

The tourist industry had a bad start to the year with the harshest winter in decades, and the lull has continued well into the summer.

At Newgrange in Co Meath's Boyne Valley – one of the island's three World Heritage Sites – just 77,292 visited in the first five months of this year, the first time in several years that less than 80,000 visited.

By comparison, the figure for 2008 was 83,102 and in 2009, 86,300.

At Clonmacnoise, the monastic site that has been proposed for Unesco World Heritage status, there has been a drop of nearly 15% in visitors over the past two years.

Between January and May of this year, just 63,832 people visitied the site, compared to 74,612 in the first five months of 2008.

One of the most popular attractions managed by the Office of Public Works (OPW) is Kilmainham Jail, where numbers have also dropped.

By the beginning of June, just 186,898 people had visited the famous prison, compared to the 212,114 that went in 2008 during the same period.

It was a similar situation at Dublin Castle, where visitor numbers dropped over 12,000 from 92,276 to 79,380 between 2008 and 2010 in the January-to-May period.

At Cashel in South Tipperary, it was the same story, with visitor numbers down more than 20,000 to 93,218 in the space of just two years, figures released by the OPW showed.

A handful of OPW tourist sites bucked the trend. These included Kilkenny Castle, the JFK Arboretum in Co Wexford, Derrynane House in Co Kerry and St Audeon's Church in Dublin.

The Department of Arts, Sport and Tourism said there were difficulties in making exact comparisons on visitor numbers but admitted there had been some decline.

"An overall drop in visitor numbers has been experienced in the current economic climate compounded by inclement weather in 2009 and the volcanic ash cloud in 2010, which led to the cancellation of bookings by foreign visitors," the department said.

Some cultural institutions, however, have seen a rise in visitor numbers exactly because of the recession. All of these attractions have one thing in common – no entrance fee.

The National Gallery, the National Concert Hall, the National Library, the National Archives and the National Museum at Collins Barracks, none of which charge admission, all experienced increased footfall in 2009 compared to 2008.