This is such a cute little town and a perfect place to spend the day.
You can wander around the old town and see all the medieval buildings. But then there are also some great Roman, Romanesque and Gothic buildings in the mix as well.
I think one of the best places to admire to city is from the famous Roman Bridge. It's a sight in itself but it also offers great views down the river and of the skyline of the old town with the church spires.