This is the oldest university in Ireland and was founded about 400 years ago (give or take a few). Also referred to as TCD.
It is located in the heart of the city and has one of the most impressive libraries in the world, mainly due to the fact that it is a listed library. The main reading room in the trinity library contains the Book of Kells, a first folio of Shakespeare's plays, an original copy of the declaration of independence posted on the General Post Office in Dublin in 1916, a harb which is old, and much other very cool stuff. As a result the largest contingent to be found in this room are middle aged American tourists.
There is a tendancy to think of Trinity students as arrogant, but this is probably just and old school new school rivalry with UCD, the truth being that both schools have their fair share of assholes and decent people.
When deciding upon a university to attend many years ago, having been accepted to all that I had applied to (lucky me), I visited the mathematics department in Trinity but it had a very funny smell and so I went to UCD.
Being an old college many stories have grown up around the place. One tells of a student who called for a glass of port during one of his exams. He had discovered the rule in some old statutes of the university that had never been updated. His port he received, however in revenge the porters threw him off the campus the following day. He had crossed the main quadrangle without his scabbard.