There is an underground parking lot in the city, just along the river, which is very doable, and will save a lot of time rather taking a bus in. The “must-sees’ are the Alcázar, the Cathedral, and the Santa Cruz barrio/neighborhood, which are all within walking distance of the underground parking lot. You will also see the Torre de Oro and some lovely plazas, which are in the same vicinity. The Plaza Nueva is also there, and the Calle Sierpes for shopping. If you have a little extra time, you may wantocosider crossing the bridge into the Tirana neighborhood, which is quaint and has many tile shops (if that interests you). The restaurants there are great too!