I can only speak to Barcelona. It’s a beautiful city, with lots of nice touristy things to do, good food, and an excellent metro system. If you get there, i recommend you walk around the old part of the city (near la rambla), but don’t see any real reason to stop on that street. It’s a nice pedestrian mall with lots of little restaurants in the street. There are lots of interesting squares around it, with street buskers, shops, and interesting architecture. I didn’t make it to La Boqueria Market because it’s closed on Sunday, which is when i was nearby.
If you want to go to Sagrada Familia (you do) book tickets well in advance. It sells out up to two weeks in advance. We got tickets for 9am, right when it opens, and that was good, as it gets much more crowded as the day progresses. We bought a third party tour, which was nice but probably not worth the money (except that there were no tickets left from the venue itself, so that’s what i could buy.)
Park Guell also requires tickets (since covid) and sells out, but only a couple days in advance. I tried using the park’s app, but it was terrible, reloading slowly every time i opened it, and it never did connect to my GPS. Don’t waste the data to download it there. (Maybe try in advance over Wi-Fi, your luck may be better than mine.) It’s only okay as a park (although there are some underused picnic benches and it would be nice to eat lunch or supper there) but has a lot of oddball Gaudi architecture that’s fun to interact with.
The cable car ride to Mont Juic was fun, and the views from the top are spectacular. We booked a guided tour for that, and it was worth it. The guide gave a lot of history and local color. (Pepa, with in&out tours, not that i know of any way to pick a guide.)
My favorite was actually the day trip to Montserrat. Get the ticket to see the black Virgin if you have any interest in the “church” part of the event, as you see a lot more of the church with that ticket, even though you just file through it. The museum is small and eclectic and a lot of fun. The best part was going up to the higher level, and walking around on the stones up there. It’s really wild, and the views are spectacular.
I didn’t book a tour, i just bought a train ticket there and admission to the site. The aerial is more fun and faster than the cog railway. Buses are much faster than the train, but i didn’t want to be confined to a tour schedule, and I’m glad i had the extra time to wander around.
I also went to the Museum of Natural History, which i enjoyed. But if it hadn’t been literally across the street from our hotel, i don’t think it would have been worth it. They are telling us to stow electronic devices, so more later.