I haven't been to the Feria in Sevilla since the days of Franco, and certainly a lot has changed since then. You don't mention your gender or age. I suspect things haven't changed so much that if you are a youngish female, some caballero wouldn't invite you to join him for a copita. We were invited to several casetas...sometimes by the women we met while walking through the fair! We would ask if we could take their photographs because they looked so beautiful, then we'd start asking about the fair, their children, their horses... If you are friendly, polite, and curious and ask the right questions "I'm visiting from ..... Could I just take a look inside so I can tell my students/friends about this fair?" I'm sure you'll get invited in!