When we visited Sagarra, a traditional and large restaurant not far off Barcelona La Rambla, it had plenty of diners but also plenty of empty spaces.
A coldish evening in Barcelona was perhaps not the best time to try ATN, a restaurant just off La Rambla. It was mostly empty and lacked atmosphere.
In Barcelona – as in Spain more generally – people eat at different times than in northern Europe or North America. It is rare to take lunch before 14.00 (2pm).