Blarney Castle is a nice spot to spend a couple of hours, of course weather permitted..UCC grounds and Fitzgerald Park are also worthy a visit, as the Cork City Gaol....Haven't been to the top of Shandon Bells, but everyone says the views of the city from there are fantastic....I just hate them because I live quite close, and they can be a little bit annoying if you are trying to sleep and someone is trying to play "don't cry for me argentina" using the bells, or any Xmas carol (even in the summer)..
Cobh is a beautiful place, but again, if it's raining, it might not be a good idea....Middleton and the destillary, you can learn a lot about irish whiskey as well as getting a free shot...I am sure there is plenty more to do, but I can't think about anything else at the moment.