Barcelona attractions/ guided tours

You don't need that. Just try to go early and get the audio guide. Much better.

I agree with Heather. We were there several years ago and arrived at both sites early and enjoyed them immensely. After our time on the main floor of the Sagrada we took the elevator to the tower & walked down the incredible spiral staircase. When we exited the Cathedral we walked the perimeter. I was mesmerized by the details of the facade. Truly a masterpiece.

Parc Guell was a wonderful memory as well. So whimsical & colorful. We had taken a Gaudi walking tour a couple days before with Runner Bean Tours. If you are a Gaudi fan I recommend this free tour. Enjoy wonderful Barcelona!

Nah, I totally agree with the above: audio guide!

Not that I don't appreciate a knowledgeable person explaining, and most importantly, answering questions, but it's indeed expensive compared to other options.

Note by the way I said "knowledgeable"... saying so because sadly in popular destinations like Barcelona, among the hundreds of tour guides in the offering, there are far too many well-intended yet non-licensed ones that are not competent enough to provide an acceptable service. This is not to say non-licensed ones can't be good, but not being licensed means there's no credential, no exams, etc ensuring he/she has a proper education on the matter so the only way you can judge is by trusting their marketing and by "reading online reviews" -and we all know that can be a flimsy way to check sometimes.

I would not just walk up to either of those sights with no ticket in my hand (or on my phone). There's a good chance you'd end up in quite a long line of other ticketless visitors, and you'd all be waiting for a time slot that had tickets available. The early time slots seem to be the most popular, so even showing up 30 minutes before the place opens would not guarantee a good result. For a visitor on a tight schedule, the only practical solution is to buy those tickets ahead of time. How early you need to do it depends partly on how picky you are about your time slot. You can go to the official websites and pretend to buy tickets ahead of time, just to see what time periods seem to sell out early, and how many days ahead of time.

Note that La Sagrada Familia is expensive, even if you just buy a plain-vanilla ticket from the official source. The basic adult ticket with audio guide is 26 euros. It's 36 euros if you want to ascend one of the towers.