Go down Calle San Gregorio until you come to the Roman Bridge. The bridge formed part of the old Roman Silver Route in the first century. Of all its arches, 15 are original (the ones closest to the city). First you'll see the Iberian boar, the symbol of the city and part of its heraldic coat of arms since the 12th century (though today it appears to be nothing more than a stone). Looking at the bridge to the left, you'll see a representation of Lazarillo de Tormes in the company of the blind man (literary characters from a famous 16th century work of unknown authorship).
We recommend crossing the bridge and continuing on the other side of the river until you reach the next bridge, Enrique Estevan bridge. There you'll have fantastic views of the city and the river (20 minutes, returning by way of the other bridge).