Cities and towns all over Ireland celebrate the 17th with parades, but since Dublin is the biggest hub, you can expect the parade to attract a crowd of over half a million spectators. In 2020, the St. Patrick's Day Parade route through Dublin runs from Parnell Square (which is north of the River Liffey) to St. Patrick's Cathedral (which is south of the river). O'Connell Street is one of the best places to snag a spot, but it gets packed early, so you'll want to arrive by no later than 10 a.m. You can also book a seat in the Grandstands instead for €70 per person if you don't want to deal with the crowds.