The Café de la Opera is located at the famous Las Ramblas and the ONLY place in that touristic area where I do recommend to stop and have a drink.
Opposite of the Opera (I guess the name says it all …), the LICEU, it is a place where you should have a coffee or (in winter) a hot chocolate with churros. All the other bars or restaurants along the Las Ramblas are simply tourist traps without any charm or particular service (and way too expensive!).
It reminds me of those old coffee houses in Viena, with an Art Nouveau (Modernist) interior. The waiters still dress like waiters and take their pride in working in such a place.
My personal favorite (but only in winter time): chocolate con churros. Or just the chocolate “suizo” which is the thick, creamy chocolate with cream on top. (calories, calories, calories, yay!)
It is perfect for a stop to rest and enjoy the interior of the cafe, have a coffee and an easy place if you need to meet up with someone in a city unknown to you.