In my youth I did a running of the bulls in pamplona, it was insane. Everyone is drinking the whole night before, the streets of pamplona are just filled with tiny little bars and everyone is stumbling around drinking and partying on the narrow cobblestones. Then you gather up in giant groups, everyone wearing white with red sashes, and run for as far as you want. Like 90% (or more) guys. I only ran like 1 km, you can exit at a ton of places and honestly most tourists will never even see a bull up close, there are just so many people and so few bulls. The bulls slide around corners a lot and its gotta confusing and frustrating for them. Everyone ends up in a giant arena where the bulls go into pens and people just hang out around the arena.
It was an adrenaline rush but I look back and think about how damn stupid I was. I was really, really into Hemingway at the time and ultimately I do have to say I don't regret it, feels like one of those things that its hard to say is a good thing to do but something I am glad I did?
The more fun festival in Spain is the Tomatina festival near Valencia, a giant food fight with tomatoes. Literally up to your belly in tomatoes, that was crazy.