May 30 in Seville is the day of San Fernando, or Saint Ferdinand. In life, he was Fernando III—the "III" because he was also king of the Spanish kingdoms of Castile and León—and he famously led the Catholic reconquering of Seville from the Moors in 1248. He died on May 30, 1252.
This may not sound terribly interesting yet, but I'm getting to the good part: Every May 30 in the Seville Cathedral, a gold and silver altar is opened to reveal none other than the preserved remains of Fernando.
The annual event is open to the public (that's how I got in). Though no photos are allowed, the video below (perhaps unauthorized) captures the official "opening" ceremony and provides a close-enough view of Fernando to make out the royal garb and kingly crown.
Note the soldiers standing dutifully by; San Fernando is not just a religious figure but a military one as well.
I can report back that San Fernando is well-preserved for a 750-year-old corpse. He is fully intact, though his skin was surely not so dry, brown and leathery in life, unless he had a secret penchant for lying out on a beach chair after a good day on the reconquista.
San Fernando left his mark on Seville (and possibly on California, whose San Fernando Valley is likely named for him). This symbol is found all over Seville (it's what's known as a rebus) and translates to "(Seville) has not abandoned me."
Legend holds that it was created out of gratitude by Fernando's son Alfonso X to award to the people of Seville for always sticking with him and his father through ups and downs. Though technically, then, a legacy of Alfonso, today sevillanos will immediately connect the symbol with Fernando III, the patron saint of the city and California Raisin par excellence.
Groups traveling on EF Educational Tours itineraries to southwestern Spain visit the Seville Cathedral—but not Fernando.