Barcelona is easily worth two days, and no one would regret having a third day (or a fourth, or a fifth…). If you can spare only one full day for the city, it will be a scramble, but a day you'll never forget.
Can you explore Barcelona in a day?
Yet, you can enjoy the best of Barcelona in a day if you plan it right. Prepare to be surprised because you will not believe how beautiful the city is. And be sure to plan ahead as this is a large city that will require some planning to see all the sites.