Beautiful Barcelona, city of contrasts and eccentricity. I went to Barcelona once before for just a day when I was in my early teens and remember being absolutely awed by the Sagrada Familia and Gaudi's other buildings in the center of the city. This time, it'll be just for a day again but someday I'll stay for longer.
Who can say Barcelona without thinking of Gaudi? I'm so excited to visit Park Guell, a whimsical fairytale world of colors and shapes. Of course that was part of the inspiration, but Spaniards love to dress well (think of Zara, Mango and Bershka) and they are not afraid of patterns and colors (Custo Barcelona). September is on the fence about whether it's in Summer of Fall so the colors are overall quite autumnal with some pops of color and there are a lot of transition pieces which can be layered as necessary.
Things to keep in mind
Although the weather stays quite warm until November, it might get cool in the evenings but dining al fresco is popular especially at the chiringuitos (or beach bars) so bring scarves and a light blazer to add and remove as necessary.
Barcelona's public transportation system is great, but the best way to experience the city is on foot, so make sure you bring comfortable shoes!