What would you do if you won the lottery? Take a luxury cruise? Go and live on a tropical island? Or would you buy a romantic ruined castle overlooking the sea?

If the castle gets your vote, but you don't know how to go about finding one, there are two options. You could put an advert in a newspaper, which is what German Helgar Schiller and his family did in 1979 - and got 60 replies. Or you could save yourself the trouble and go to an auctioneer specialising in unusual properties - the same German family, now turned estate agents. They are Schiller & Schiller in Co Sligo. When the Schillers decided to buy a castle 20 years ago, they didn't fancy a schloss in their native Bavaria, and looked first in Canada (too many snakes and not enough castles) before realising Ireland was the perfect location. Helgar and his wife Erika were captivated by the ruined walls of Ardtarmon Castle and the spectacular views overlooking Sligo Bay. When it was first built in the 17th century by Sir Francis Gore (a distant ancestor of Countess Markievicz, who lived in nearby Lissadell House) the castle commanded the sea approaches to Sligo town. Renovating it took 15 years, and the castle is now home to the family and their two businesses: real estate and self-catering apartments. The restoration was faithful to the original, with rebuilt turrets, massive oak beams, stone floors and ochre exteriors, but modern-day comforts, such as underfloor heating, have been added.

Many of the Schillers' clients are German, Swiss and Austrian. "They feel more comfortable with us because of the language. They trust us," says Bjorn Schiller. Established in the early 1990s, the business is now run by Bjorn, 26, and his sister Bianca, 33, since the death last year of their father in a plane crash at Strandhill, Co Sligo. When prospective buyers of ruins see the renovation of Ardtarmon Castle, it encourages them to buy, says Bjorn, because they can see what can be done. One German dentist bought a ruined Church of Ireland rectory near Lissadell House through the Schillers in 1994, because, he says, there were not many Germans in the area. Then, there was "nothing inside, no walls, no ceiling, only a staircase and trees", but three years later it was a beautifully restored home with a conservatory and landscaped garden. Specialising in properties with lake, sea or mountain frontage, the Schillers also sell manor-type houses, ruins and small stone cottages. The map of Ireland, in their little private office in a corner of the castle, is dotted with yellow stickers from Killybegs in Co Donegal to Castlecove in Co Kerry. Properties currently on their books include a two-acre site with a helipad and planning permission for a £65,000, six-bedroom house overlooking the sea near Ballycastle, Co Mayo; a renovated cut-stone two-storey house on two acres with a river, in the Arigna mountain range in Co Sligo, for £125,000; and the ruins of Rahelly House, near Ben Bulben, for £300,000.

Schiller & Schiller's listings information is clearly aimed at foreign buyers - although it is interesting to know that a house is near Queen Maeve's grave or that wild flowers grow in the garden, it is hardly likely to impress an Irish buyer. Their website, though, attracts a different type of housebuyer, says Bjorn - Irish people living and working abroad, in places such as Hong Kong and Australia who are looking for retirement properties. The family's access to the European market means they can realise higher prices, according to some residents of Co Sligo who monitor the local housing market. One English couple, the Stevensons, were advised to sell their old stone cottage for £26,000. "We decided to use Mr Schiller because he valued it at £37,000 - which is what it sold for six weeks later," says Pat Stevenson. The house was bought by a German family, who intend to spend three years restoring it before moving to live in Ireland permanently. Typically, a European looking for a holiday or retirement home in Ireland will look first in the heavily-promoted areas of Galway and Kerry, says Bjorn, but "they are willing to travel, to look around, and the north-west is becoming more popular, especially since the ceasefire in the North".

Another change in the country house market is that spiralling housing costs in the capital mean increasing numbers of Dubliners are moving to the west. According to Bjorn "It used to be foreigners, but now it is Irish people who are pushing up house prices in the west. Selling an ordinary house in Dublin gives you enough to buy something special in the west. I have clients who have sold their houses in Dublin, bought in the west, and now rent in the city." So buy that lottery ticket now - or sell that Dublin home - and it could be you restoring the spectacular ruined manor house in the shadow of Ben Bulben.