What is it like to have strangers poking about in your drawing-room, peering around the door of your bedroom or eyeing the silver? For those who have thrown open the doors of their castle to the public, the influx of visitors could be at best an inconvenience, at worst a diabolical intrusion. Surprisingly, however, most stately home owners are not only philosophical about their economic need to let down the drawbridge, they actually seem to enjoy showing people around.

Samantha Leslie, in her early 30s, runs Castle Leslie, in Co Monaghan, with the help of her partner, Ultan Bannon, and supported by her father's brother, Sir John Leslie - known also as Uncle Jack. Tall, urbane and always willing to talk about the house in which he was brought up, 80-year-old Uncle Jack is king of the castle, guiding parties of visitors round the house several times a day.

"One of the really pleasant things about having people staying in the house," he says, "is that it is so informal. You don't have to dress for dinner nowadays." This from a man who packed a dress suit for the Normandy landings, believing he might be able to take in a few shows while he was in Paris. "And, of course," he continues, "it's a house that was built for entertaining so we like lots of people in it." Since Samantha took over five years ago, Castle Leslie has been re-roofed and rewired.

"We got a grant from the government," says Sir John, "for the re-roofing. It needed three tonnes of new lead. The grant covered half the cost and the rest we got from the sale of 80 oak trees. Some of the timber went to repair Windsor Castle and the rest went to Dublin Castle." Castle Leslie harbours many treasures, including Belgian tapestries and Persian carpets - but what people usually want to see are the family things such as Winston Churchill's baby dress, the piano Paderewski played on or the bed once occupied by one of Napoleon's paramours. Nothing is under wraps. You may even get to sleep in the bed - if you're in the right bedroom - and you can certainly play the piano.

Further, if there's a bit of late-night music and drinking going on in the drawing-room, Samantha and Ultan are often in there in the thick of it. Sir John has no worries about security: "We're well protected," he says. "The very best silver is in a cupboard with an iron door which weighs a tonne, and we have an alarm system that goes directly through to police headquarters; though it does sometimes go off when the cat goes up the stairs."

Desmond FitzGerald, Knight of Glin, is similarly relaxed about the treasures of 18th-century Glin Castle. "We don't bother getting nervous. We have people staying overnight regularly and in July and August we rent out the whole castle." His wife Olda agrees: "We tell people it's our home and if they want to have a wild time, this isn't the place. There's no bar, for instance." The family lives in a separate wing and often goes away altogether when the castle is rented out. People, it seems, feel a bit nervous in case they're sitting on a chair they think they're not supposed to be sitting on. "They're paying a lot of money and they want peace and privacy," says Desmond FitzGerald. "They don't want us around." Occasionally, he himself will give a guided tour of the castle and its art treasures but usually only to specialist groups.

The upkeep of Glin is enormous - there are 20 bedrooms in the whole castle - and Desmond FitzGerald is committed to making the house pay for itself, as far as possible: "We get a government grant for the building, plus some help with restoring the furniture, and if you receive assistance, you have to give something back." His only problem is that sometimes people expect the castle to be open all the time.

"We're open 60 days a year but closed when the whole castle is rented. We could never keep going on the income we get from being open to the public so we have to get the balance right. Doing it this way, we manage to employ about 100 people."

Glin Castle, with its gross of bedrooms, its decorative plasterwork and collections of Irish furniture, may be among the most significant of our great Georgian houses but in Co Cork, the gracious, 18th-century, three-bedroomed Dunkathel House in Glanmire is also an important part of Ireland's Georgian heritage. Formerly the home of Cork merchant Abraham Morris, it is now home to the Russell family.

Betty Russell, who lives there with two of her sons and has grand-children around the house as well, is delighted when there are visitors, despite the fact that it means the family's personal life is on display. There's no lying on in bed on certain days: "We show people round the house twice a week. They see everything in the house, including our bedrooms so we've got to make sure the beds are made and everything's tidy," she says.

At the turn of the century, there was about 2,000 big houses. Now there is no more than 30. Westport House is one of the few that has survived in the west and has done so by initiating a number of projects including a camping and caravan site, a boating lake and a small railway. Jeremy Altamont, Marquis of Sligo, opened up Westport House in the early 1960s: "In those days, I used to go on television a lot and people often recognised me but now not so much. They're more interested in what's going to happen to the house."

The family has no problem about their home being made public: "Four of my daughters are involved in the running of Westport House," Altamont says. "That's what makes it such a success, the fact that it's a family home. People see us around the place." One of his daughters has a flat in the house but the family lives in a house on the estate so privacy for them is not a problem.

OPENING TIMES: Castle Leslie: Tours on the hour Sunday to Thursday, 2p.m.-6p.m. until August 31st only; admission £3.50. B&B and evening meal all year. Current offer: two nights B&B plus one evening meal £99 pps. Phone 047 88109 and www.castle-leslie.ie Castle Glin: B&B (from £105 pps) and castle rental (from £11,100), all year. Castle open May-June only. Phone 068 34112. Westport House: House and zoo etc. 10.30 a.m.-6p.m. until August 23rd after which times vary. Phone 098 25430 for details. All-inclusive family ticket £21. Dunkathel: May to mid-October Wed-Sun 2p.m.-6p.m. or by appointment; admission £2. Phone: 021 821014