A must for the kids, the old Synod Hall, added to Christ Church Cathedral during its late-19th-century restoration, is home to the seemingly perennial Dublinia, a lively and kitschy attempt to bring Viking and medieval Dublin to life. Models, streetscapes and somewhat old-fashioned interactive displays do a fairly decent job of it, at least for kids.
The model of a medieval quayside and a cobbler's shop in Medieval Dublin are both excellent, as is the scale model of the medieval city. Up one floor is Viking Dublin, which has a large selection of objects recovered from Wood Quay, the world's largest Viking archaeological site. Interactive exhibits tell the story of Dublin's 9th- and 10th-century Scandinavian invaders, but the real treat is exploring life aboard the recreated longboat. You can also climb neighbouring St Michael's Tower and peek through its grubby windows for views over the city to the Dublin hills. There is also a pleasant cafe and the inevitable souvenir shop.