When Desmond and Mariga Guinness first lived here in the 1950s, they were unlikely champions of Irish architecture. Mrs. Guinness, the daughter of a German prince, had grown up in Europe and Japan, with no real link to Ireland. And although Mr. Guinness had Irish roots going back more than two centuries, he had been raised and educated in England (Oxford, class of “˜54). But he was a Guinness, descended from the 18th-century brewer who put the family name on the lips of stout drinkers the world over. His father, Bryan Guinness, Lord Moyne, kept a home in Ireland, and by the mid-’50s his mother, Diana, one of the famous Mitford sisters, was living in County Cork with her second husband. And Ireland’s long economic decline had made property far more affordable than in England, making it an attractive alternative for the young couple, who moved across the Irish Sea in 1956. In the two years they spent searching for a home, driving through the countryside and making regular forays into Dublin from a house they rented in County Kildare, the Guinnesses became familiar with the country’s architecture “” particularly its 18th-century buildings, from grand country homes to town houses filled with working-class flats “” and found themselves increasingly bothered by its state of decay. And given that they did not have to work for a living (Mr. Guinness lived off family money), they were in a rare position, they realized, to do something about it. In February 1958 they announced plans to re-establish the Irish Georgian Society, a group that had created a photographic record of Dublin’s best Georgian buildings earlier in the century; this new version, Mr. Guinness wrote in The Irish Times, would “fight for the protection of what is left of Georgian architecture in Ireland.” The following month they began restoring a building of their own, Leixlip Castle, a dilapidated 12th-century fortress on 182 acres west of Dublin, which would be their home and the group’s headquarters.