The National Library of Ireland, located on Kildare St, house a beautiful reading room. A geneology service is also available here. The library is only a short walk from Stop 4 on the Hop-on Hop-off tour.
"Trinity College Library, Dublin - the smell of old books is amazing : )" Is there anything as beautiful as a library? And just think, at this point if you started reading that library, you would not live to finish it. At least, not at my speed.