Salamanca is most famous for its university, but it was its two cathedrals that impressed me the most. The interior of both, filled with tombs of old clergy and paintings, is nothing too special, but I would recommend the Ieronimus exhibition whose entrance is located at the side of the cathedral. It costs extra but is worth every penny. It allows you to go on top of the cathedrals and gives spectacular views of both the city and the cathedrals.
My father and I visited this WHS on our last day in Spain. In addition to the university and cathedrals, we also stopped by the Roman bridge (nothing spectacular) and visited the church of San Esteban with its beautiful cloisters. A cursory look at the Plaza Mayor was also made. We had not originally planned to go to Salamanca, but we are glad we did. It would have been a tragedy to skip this place for a day of relaxation in Madrid.