If you're traveling by train or bus, you'll most likely pass through Busaras. This terminal is a major transportation hub for the area and an attraction in its own right.
You'll be spoiled for sightseeing choice when visiting City Centre Dublin. Busaras is a great place to start here, but there are many other fine places to explore. Guinness Storehouse, Trinity College, and Aviva Stadium are close to the transportation hub and and will cap off your day nicely.