St Michan's Church - One of the top visits we all had, thanks to a Michael Palin-ish tour guide (with a touch of Hitchcock). St. Michan's has catacombs underneath the church, where you can see the mummified remains of 4 individuals, including a crusader. There are other bits of history, including the remains of brothers from the 1798 rebellion (and their execution orders) and a gorgeous organ that Handel may have played early performances of The Messiah.
Kilmainham Gaol - Dublin, Ireland. This famous prison on Inchicore road closed its doors to prisoners in 1924, and today is home to a ghoulishly interesting museum, with exhibits on the terrible prison conditions and tours around the spooky dark corridors and dank cells. This is the place where the leaders of the 1916 Easter Rising were executed, and scenes from The Italian Job were filmed in the main hall. Entry is €5.30.