Starbucks at the Diagonal Mar is located in its' own unit within the mall, right by the Food Court area, the interior is pretty and feels recently refurbished and has lots of comfortable seating in the form of a long communal sofa.
I visited this location twice during my recent trip to Barcelona - on the first occasion, I was turned away as they didn't have any ice, which seemed insane as I visited during the peak of summer with temperatures over 80 F!
I visited again the following day, as the mall featuring this Starbucks was right across the way from the Hilton, where I stayed during my time in the city, and I was pleased that the ice issue had been fixed and I was able to order an Iced Vanilla latte.
The baristas were friendly and did speak basic English on both occasions; they were able to explain and apologise for the ice situation in English and I could order in English.
Beverage quality was consistent with other Starbucks locations I visited during my trip to Barcelona, I generally found standards to be poor overall, the coffee was rather milky and wasn't very strong. I did like the fact it was served in an actual glass, however, which felt more suitable and welcoming for sitting in than the plastic cups they tend to use everywhere else.
Prices were also higher than back home in the UK - with international Starbucks cards such as those from the UK and US not accepted.
The opening hours are very reasonable - they close at 9 pm daily, including on Sunday's when the stores are actually closed which is handy if you're in the area and fancy a coffee - especially if you're visiting the nearby beach or staying at the Hilton Diagonal Mar (as I was during my stay) 3* read more