If you’re finalising your plans for a weekend in Dublin, try and centre it on mid-October. For one weekend every year, some of the capital’s finest buildings, old and new, open their doors to the public for free, to provide an insight into their structure and substance, past and present.

Two of Dublin’s older buildings, still in use but closed off from the public day-to-day, should be on your list on the weekend of Open House Dublin, 16-18 October, provided they’re on the list again.

Number 58 (formerly number 30) Merrion Square was home to one of Ireland’s most famous politicians, Daniel O’Connell. Now home to the Dublin branch of America’s Notre Dame University, this building was built in 1762 as part of the Fitzwilliam estate on Merrion Square, modelled on the quiet squares of Paris. This three-bay, four-storey-over-basement house is neo-classical in style, and on Open House weekend, gives visitors a glimpse of the rooms and life that O’Connell and his family once had. Among the highlights are the stained glass chapel and the library, which contains a vast collection of Seamus Heaney’s work, a sketch of W.B. Yeats and an iconic photo of Samuel Beckett.

The highlight, however, is the view of Merrion Square, opposite the house, and the city beyond. One can see for miles and appreciate how low-rise and close everything is in the city. The staff of Notre Dame, which has been based here since 2002, will undoubtedly be as welcoming and informative as last year.

Just three blocks away, built twenty six years earlier, is Iveagh House, headquarters to Ireland’s Department of Foreign Affairs and Trade. This vast building, once two houses, is defined externally by a four columned entrance portico, inspired by St Paul’s Cathedral in London. Originally the town mansion of Bishop Clayton, it was bought by Benjamin Guinness in 1862 and remained part of the Guinness family’s empire until 1939.

As a part of the world of international diplomacy, it’s fitting that splendour and style define much of the interior. Visitors can marvel at fine paintings, some donated by visiting dignitaries, and the plush offices in, and views from, this Portland stone building. The staircase is defined by Victorian ironwork, marble columns and circular roof lights. There’s a feel of decline about the ballroom, but it remains an elegant presence, full of light and impressive features.

These two buildings’ raisons d’être have changed greatly since their earliest days. O’Connell lived in Merrion Square till he died in 1847, but his family was left with little money and soon had to sell the house. The donation by the Guinness family of Iveagh House to the State marked the family’s parting with another part of its Dublin estate. Both O’Connell and Guinness would probably be pleased that their pride and joys are accessible to all for an autumnal weekend every year.