About the Fiestas de la Calle de San Sebastián The Fiestas de la Calle San Sebastián is the unofficial closing to the longest holiday season in the world. During the multi-day celebrations, Old San Juan is completely taken over by live music, impromptu dancing in every street corner, and even circus performances! Fun fact: The festival is also known locally as the SanSe, a shortened version of the full name.