CrossFit Alpha Link is located within walking distance of the Air BnB we stayed in while in the Gracia neighborhood of Barcelona, Spain. This modest sized CrossFit box did not respond to my initial emails however they took me right in when I dropped in so I would give it a try if you run into the same problem. The class was taught in English and was wonderfully brutal with the workout featuring a bear complex ladder. Class size was just a handful of people, all of whom were friendly and welcoming. If you're staying in Gracia, I would recommend trying out Crossfit Alpha Link.
As souvenir t-shirts go, this one isn't as exciting since it doesn't say, "Barcelona" or "Spain" or something that more obviously commemorates this Barcelona CrossFit experience. Even so, I still love wearing it as it nonetheless reminds me of my Barcelona drop-in.
Remember CrossFit Drop-in Etiquette: Contact the box in advance, be courteous, and have a great time.