Late last June I was in Burgos during the Fete to San Juan, it is a heady, noisy event with fireworks at midnight and as many broken bottles in the streets at 6am as one finds during San Fermin in Pamplona. I've also done the wine festival in Viana during the middle of June, it is a lot of fun and features great local wines. There are many villages along the way that feature bull runs and fights, Sahagun and Puenta la Reina are two that come to mind, the one in Puenta la Reina features traditional costumes and dancing and the folks who live along the main road through town on the Camino set up shop behind the barricades with family picnics and feast. Astorga has a festival in June that makes it almost impossible to walk on the Camino, if you are trying to find shells and waymarkings. I ran into a festival for San Juan in Najera last year which was attended mainly by young people in a "coming of age event," the downside of this event was most of the roads were closed and I was riding a bike. Bottom line you can find some sort of local festival on just about any weekend during the summer in Spain.