Like many of the colleges I believe it’s only possible to visit Trinity outside normal term times. As of 2019 there’s a very reasonable £3 entrance fee. There doesn’t appear to be a price for concessions. The three main things to see are the chapel, the dining hall and the gardens which are all quite lovely and are shown in the photos.
The chapel at Trinity College is in a league if it’s own. The historic woodwork is a must see if you’re interested in woodcarving. Some of Grinling Gibbons finest work. Simply stunning!