Guernsey is a tender port and the ship leaves early at 2 PM so we just walked around town but we found out that there is a bus at the dock that will take you around the island for one pound. The people who had taken tours really enjoyed them and I would have liked to have more time in Guernsey but the ship went to Cork next and needed the time to get to the port.
In Dublin we walked around town visiting St.Patrick's Cathedral and Trinity college seeing "The Book of Kells" and Dublin's oldest pub on our own. I would recommend taking the HOHO since Dublin is such a large city for walking. The line for "The Book of Kells" was quite long but moved quickly & in 30 minutes we were inside. There was a Shakespeare Festival going on at Trinity but nothing on Monday, the day we were there.
In Belfast we took the HOHO which was well worth it. There was a discount given for Princess cruise people. We saw the many murels around town from the bus. There is a new Titanic Museum that some people went to and liked. You had to get there early for the timed tickets. Belfast is a nice walking town and the shop people were very friendly.