When rain sets in over Dublin, stay within the Georgian core rather than crossing town. The National Gallery of Ireland on Merrion Square West is free to enter and large enough to absorb two hours, with a good café downstairs. A short walk away, the National Museum of Archaeology on Kildare Street holds the Ardagh Chalice and the bog bodies, and admission costs nothing. Both are busiest between 11am and 2pm, so arrive at opening or after 3pm. If you are staying near Connolly or Heuston station, the Luas tram links both to the city centre in under fifteen minutes, which keeps you out of the rain for most of the journey.
Dublin: spend the wet hours in the city centre
Push further west and the Guinness Storehouse at St James's Gate is the dependable indoor block, though you should book a timed slot online the day before, as walk-up queues are long on wet Saturdays. More rewarding for a quiet afternoon is Marsh's Library beside St Patrick's Cathedral, a seventeenth-century room that costs a few euro and takes forty minutes. Glasnevin Cemetery Museum, two and a half kilometres north, runs guided tours that continue in light rain under umbrellas. For families, the Ark on Eustace Street in Temple Bar runs children's exhibitions and workshops; check opening days before travelling across the city.
Cork and Cobh: a harbour day under cover
Cork city rewards a wet day better than most visitors expect. The English Market off Princes Street is fully covered, free, and worth ninety minutes of browsing between the cheese stalls and the upstairs Farmgate café, which does a good lunch. From there, the Crawford Art Gallery on Emmet Place is free and strong on nineteenth-century Irish painting and sculpture. If the rain is heavy, skip the walk to Fitzgerald's Park and take a bus or taxi instead to Blackrock Castle Observatory, about four kilometres east along the Lee, where the exhibition is indoors and the tower café looks back over the harbour.
Cobh, twenty-five minutes by train from Cork Kent station, is the best rainy-day excursion in the region. The Cobh Heritage Centre beside the railway station covers emigration and the Titanic's final call in about an hour, and St Colman's Cathedral above the town is open to visitors and worth the climb even in drizzle. Combine the two and you have a half-day that needs no car. If you are based in Cork for two nights, book a hotel within walking distance of St Patrick's Street rather than out by the airport, since the city's wet-weather options are clustered in the centre.
Galway and the west: tours, buildings and short hops
Galway's wet-day answer is the city itself. The Galway City Museum behind the Spanish Arch is free and covers the region's archaeology and fishing history in about an hour; the Spanish Arch and the Claddagh are a two-minute walk. The Hall of the Red Earl, a medieval excavation preserved under glass off Druid Lane, is a short stop that most visitors miss. For a longer block, the Cathedral of Our Lady Assumed into Heaven and St Nicholas on Abbeygate Street are both open daily and free to enter, and the latter has connections to the Lynch family that shaped the town.
Beyond the city, take the bus to Salthill and spend the wet hours in the leisure centre rather than on the promenade. The Connemara coast is a poor choice in heavy rain, but Kylemore Abbey, roughly an hour and a quarter by car from Galway through Letterfin, keeps its house and church open and the walled garden is viewable from the covered paths. If you plan to use Galway as a base for several days, a hotel near Eyre Square puts you within reach of the coach station, which matters when you would rather not drive in poor visibility.
Kilkenny and the southeast: short, dense and walkable
Kilkenny is the best wet-weather town in Ireland because everything is within five minutes of everything else. Kilkenny Castle, the medieval mile's Rothe House and St Canice's Cathedral sit inside a compact loop, and the castle's furnished rooms take an hour and a half. The Butler Gallery in the old Evans Home on John's Quay is free and adds another hour, with a good café. Rain here rarely lasts all day, so plan two indoor stops and one short walk between them rather than a full schedule.
For a longer stay, use Kilkenny as a base and take the train to Waterford, about forty minutes, where the House of Waterford Crystal runs factory tours that are entirely indoors. Book the first tour of the day to avoid coach groups. Skip the Rock of Cashel in persistent rain; the exposed limestone gets slippery and the views, which are the point, disappear. If you want one recommendation, I would book two nights in Kilkenny city centre in spring or autumn, when the rain is lighter and the indoor sights are quieter than in July and August.
