I lived there for 6 months so trying to remember whats good...
Salsa bar called el bombon was fun if you wanna dance. Nevermind was pretty cool inside. Billy brunch. Explore around Poble nou and then head to the beaches up north. Bogatell was my fav, Mar Bella was a nudie. Stay away from Barcelonetta so dirty and pickpocket friendly.
Kinda basic but a hike up to Bunkers del Carmel is a must, watch the sunset, bring some drinks and food and chill there one evening. I spent a lot of nights there. You have the best view of the city for sure. Montjuic is great too. And also around Tibidado, gorg houses, a bit far out.
Watch out for Humana sales! depending what time of the month you could make it during their descending 5 euro, 2 euro, 1 euro or even 50 cent days. Everything in store super cheap, but it's also busy.
Sagrada Familia is free if you go on Sunday for mass, but you have to be there early, around 8am.
Nice art scene in Gracia and Poble nou, you'll find nice cafes and bakeries around there too, and in Exaimple
Best bars were in Raval and sometimes Gothic, gets fun at night!
That's all I can remember tbh, and I was there during covid so didn't do a load of restaurants or clubs etc etc, but you'll find nice stuff for sure :)