You can get to Trinity College in a variety of ways:

Dublin city centre map
Outer Dublin map
For more detailed instructions, visit http://www.tcd.ie/Maps/tcd_directions.html

• TAXI from Dublin Airport (20-30 minutes) - approximately 25Euros
• AIRLINK BUS to Dublin City Centre (30-40) minutes - approximately 5Euros one way - Map of Bus stops
  (http://www.dublinbus.ie/your_journey/airlink.asp)
  Route 747 (every 10 minutes) - stops at O'Connell street (main center of Dublin) - 15 minute walk to Trinity College
  Route 748 (every 30 minutes) - stops at Tara Street Train Station (on the river Liffey) - 5-10 minutes walk from Trinity College