The St. Sebastian's festival in Olvan is an ancient town vow maintained since the Middle Ages. Originally, the meal was intended for the most needy, but over time it has transformed into a major popular celebration in gratitude to the saint for having freed the inhabitants from the plague.

The central event of the day is the cooking of rice paellas distributed among all attendees. The traditional lunch, which can be eaten in the square or taken home, includes a plate of rice, sausage (botifarra), an orange, bread, and wine. Although it is free, participants are asked to collect tickets beforehand at the Town Hall or local establishments to guarantee their portion.

Besides the rice feast, the festive day begins at 10 am with the opening of a market with various stalls. At 11 am, there will be a mass sung by the Coral Estel, followed by the procession, the singing of the Goigs de Sant Sebastià (Joys of St. Sebastian), and the adoration of the relic.

Community involvement is one of the most unique elements of the festival. The celebration is financed thanks to contributions from individuals and businesses in the municipality and surrounding areas, and the neighbors themselves are responsible for preparing the meal. Since the previous day, numerous volunteers dedicate themselves to cleaning and preparation, and on January 20, they organize the cooking and distribution.