Three Days in Barcelona
I should preface this post by saying I am by no means an expert on Barcelona. My AP Spanish class six years ago left me with the ability to point at things and mutter random words like "el baño" and "sangria por favor," so needless to say, I can hardly pass for a local. Prior to going to Barcelona, however, I did have the foresight to contact my friend Aleix, who is from the area and gave me some truly incredible recommendations. Much of this post and the success of the trip is thanks to him and to the fastidious planning of my travel companions Tamar, Elsa and Hannah.
The three days that this post suggests doesn't include travel days, and though the time in each place could be extended if you were staying longer, I don't know that I'd recommend trying to fit more per day or you'd be absolutely exhausted. Don't forget comfortable shoes.
Day One
Morning
After breakfast, walk around the Gothic Quarter! Streets are narrow and packed with shops and interesting features so it's best to give yourself time to wander and explore. The architecture is truly stunning and you should definitely see Santa Maria del Pi, Plaça del Rei, Palau Güell, Pont del Bisbe, Santa Maria del Mar, Plaça Reial, and the Cathedral of the Holy Cross and Saint Eulalia (also called the Barcelona Cathedral). Note if you want to go inside the Cathedral that it is a practicing church and shorts or exposed shoulders are not allowed.
Afternoon
For a quick and easy lunch try Bacoa Burger (multiple locations, but there's one in the Gothic Quarter). There are veggie/vegan options and the burgers are massive and delicious. They also do an intriguing "burger bowl" on a bed of lettuce if buns or gluten aren't your thing. People generally don't eat lunch in Spain until between 13:00 and 15:00.
After lunch wander around the boutiques and shops in the Gothic Quarter (there are more than I could possibly list here). The logic of when stores were open vs. closed never really became clear to us, so if there's a particular store you want to go to make sure to check in advance whether it will be open.
After browsing, head toward La Rambla and La Boqueria (prime targets for pickpockets according to my friend Aleix so keep your eye on your bag). La Boqueria is a massive food market that dates back to 1217, and is packed with stalls selling fruit, fish, cheese, and meat. Buy some snacks to hold you over until a late dinner (21:00 to 23:30 usually).
Evening
For dinner, head to Caravelle (in El Raval) for tacos, cocktails and beer brewed in house. Maybe not the most authentically Catalonian place, judging in part by the British staff and English-speaking customers, but the food was great and the beer and cocktails were truly top-notch. Who could say no to a hibiscus margarita? They also do a very well-received brunch every day of the week.
After dinner, if you're feeling up to it, Foxy Bar is nearby. The staff are friendly, the atmosphere is cozy, the decor is interesting, and, most importantly, the drinks are cheap.
Day Two
Morning
Go see the exteriors of two of Antoni Gaudí's most famous buildings: Casa Milà (also known as La Pedrera) and Casa Batlló. Tickets to go inside are expensive, so if you're on a budget I recommend doing some research and picking the one you're most interested in (and buying tickets in advance online). I chose La Pedrera and it was definitely worth the €16.50 I spent on a student ticket. The ticket price includes a headset-guided tour which explains the building's fascinating history, and the view from the roof is absolutely stunning.
Afternoon
For lunch try Flax & Kale for healthy (but delicious!) food. About 80% of the menu is plant-based and the other 20% contains fish. Afterwards walk around the streets of El Born, where there are countless interesting shops and boutiques. When we were there the workers at the Picasso Museum (and certain other museums) were on strike, but if the strike is resolved when you are there the collection is meant to be incredible. (Technically you are allowed in during the strike, but that would involve crossing a picket line.)
If it's warm out, go to the beach! I recommend Nova Icària - we chose it because it's a little further from the city centre, but still a short/inexpensive taxi. According to the reviews we read online it's where most locals go, and that's definitely the sense we got from being there. We arrived around 15:00 and left at 18:30 and it was absolutely beautiful - just crowded enough for fun people-watching but not so crowded that we were tripping over people.
Evening
Tapas! Finally! There are about a million tapas places in Barcelona, so I can only speak to my experience here, but we loved Palosanto (El Raval). The tapas were incredible, the (very good) sangria was extremely cheap, and the atmosphere felt cozy and bustling at the same time. I should also mention another tapas place multiple people recommended that I didn't have a chance to visit: El Xampanyet in El Born.
Day Three
Morning
In the morning go to the Sagrada Familia - it's busy at all times of day, but we hoped by getting up early it might be somewhat quieter? Who knows, but it's definitely worth it to go inside so make sure to buy timed-entry tickets in advance online. You can spend a bit extra to go up in the towers, which would be very cool but was out of our budget. There's a dress code as well for the Sagrada Familia but it's much less strict then the Barcelona Cathedral - as long as you don't have crazy cleavage or your butt hanging out your shorts you should be fine.
Afternoon
After the Sagrada Familia head over to the Gràcia neighborhood and wander around the shops and squares there. Get lunch at La Pepita - more tapas! We went on a quiet weekday and the place was still packed by 14:00. After lunch, go to Park Güell, an absolutely massive public park designed by Gaudí. Entry to most of the park is free, but you will likely want to buy (in advance!) the 7.50€ timed tickets which get you entry to the park's "Monumental Core." Plan to spend a few hours in the park as there is lots to explore!
Evening
For a relaxing (and rejuvenating!) final meal go to Teresa Carles, the sister restaurant of Flax & Kale. I am honestly still thinking about the quinoa salad I had there. I know I've just said flax, kale, and quinoa in the same sentence which is probably off-putting for many people, but there are incredible options even for people who balk at words like "spirulina" and everything really does tastes delicious. The house wine is also well-priced and very good. The restaurant is working on an English-language version of their cookbook and I plan on buying it the second it's released.
If you're going or thinking about going to Barcelona I hope this has been helpful in some way! A lot of what I've written is probably in every guidebook, but let me know if you go to any of the restaurants!