As a 4th (going to 5th) year student, I have faced several highs and lows throughout university. Before coming to Barcelona, I had worked at two internships, one in Puerto Rico and one in New Jersey. Even though I have this experience, why did I choose to continue on to doing an international internship in Barcelona?
Initially, I really wanted to leave my comfort zone and do an exchange but I wasn't fond of being such a long time studying away from home and I also thought of vacationing here but I wouldn't be ale to live like a local. So doing an international internship was the best of both worlds.
I'm an engineering student and I came here for 10 weeks. Work culture here in general is very different than in PR and the US and it's great to have been able to experience it.
Barcelona is an amazing city with a relaxed feel to it. There's something here for everybody, although a lot of tourists come to Barcelona, living here for the summer immerses you to find opportunities to do things that locals do and see how people live as oppose to what you're normally used to.
Things you must do: Eat tomato bread (ask a local to see if they can teach you how to make it) and olives, visit "Los bunkers de carmel", go to Barceloneta beach, Castelldefels beach, Sitges beach, Shop at local markets (the closest one near me was Mercat Hostafrancs near Sants. La boqueria and Mercat Sant Antoni are some of the larger ones), get bread at bakeries, find festivals (The intern group guide suggests many of them and they are worth it!), museums are great too, and many more things.
My recommendations: Come to Barcelona with an open mind to any problem that comes, there's always a way to communicate and find a solution and you'll get the most enjoyment and learning out of being here. Planning out your weeks will help a lot but have flexibility in case anything pops up last minute.