Busáras is the headquarters of Ireland's national bus service, Bus Éireann, and is located on Beresford Place, behind the Custom House on Dublin's north side, and adjacent to Connolly Station, one of Dublin's two main train stations. From here, bus services radiate throughout the country.
The building was designed by celebrated architect Michael Scott and is today subject to both praise and derision. Some see it as a landmark of modern Irish architecture, and others have actually waited for a bus in it. It is certainly possible to detect modernistic flourishes such as the curvy, fan-shaped roof piece, but on the whole it has not aged well, and has certainly not been kept in good nick, inside or out.
On the whole, a building you visit only out of the necessity of reaching a more picturesque part of the island.