Take the bus to the city center and walk along the city's main park, the Esplanadi. There are cafes and shops on either side. Then go to the market at the end of the Esplanadi and get some good fruit or fish or any of the stuff they and and go just behind that to Senate Square, sit on the steps of the huge chuch there and eat it. If you have time you can take a boat over to over to an island only 10 minutes away which is also fun. Depends on how your time is going, but there is lots to do. I've been there twice and love it.