Kildare Steam Museum mentioned by Metrovik: https://www.steam-museum.ie/
They reduce their opening hours in the off-season but the website says they're open Sundays and Bank Holiday's in October, so you're in luck @MoI_PMB
Its actually very close to the Dublin Cork railway, and once upon a time there was a station in Straffan. The village itself is small, but there's a few interesting spots nearby including the grave of one Arthur Guinness. The weather may be a bit damp this weekend, otherwise I'd recommend renting an ebike and heading there along the Grand Canal - its very doable from Dublin, or you could get a train down to nearby Sallins and cycle up from there.