In medieval times churches and cathedrals, often collected relics, this was meant to attract pilgrims and add a source of income to the churches. They were not always genuine and the supply of these artifacts was big business.
Genuine or not, the museum at the cathedral holds two relics, here is the silver case holding a bone from San Servando.
the business of the relics at the Medieval times was very important. A good church or cathedral with a relic had a promising future and many incomes. Here the one in Cadiz had two, this one is from San Servando, and no, I have no idea who was him lol
The other relic is the Blood of Santa Victoria, a glass jars with some staining within it. Its set at the foot of a statue of the saint.