There isn't really an awful lot of interesting stuff to see in Dublin, in my opinion. I think of all the places I've been it's been the most disappointing, in that regard.
The fact that the Guinness museum is undoubtedly one of the main attractions says it all ...
it is hard to see a lot in 7 hours. However, Dublin was once known as the second city of the British Empire after London and has many imposing buildings. Stick to the city centre around the River Liffey and stroll around to St. Stephens Green Park. Nearby also is Trinity College, Government Buildings and Dublin Castle. There are many more places. I enjoyed a recent visit but 7 hours is all too short. Enjoy your trip.