Dublin starts here, on the ridge above the Liffey where the Vikings beached their longships and the Normans built in stone. This is the medieval city — older than everything Georgian, smaller than you expect, and still legible if you know where to look.
Begin at Christ Church, the oldest building in continuous use in the city, founded around 1030 and rebuilt by Strongbow's Normans. Go down to the crypt for the mummified cat and rat and the cathedral's quiet underbelly, then cross the covered bridge to Dublinia in the old Synod Hall. From there it's a short drop to Wood Quay — the riverbank where Dublin literally began, excavated in the 1970s and then, infamously, paved over with civic offices despite the protests.
Down Fishamble Street, where Handel's Messiah had its première in 1742, and up to the Brazen Head, which insists it has poured since 1198. End along the river boardwalk at the Ha'penny Bridge, cast iron and 1816, and cross to the Luas at Jervis with the old skyline behind you.