Student or Learner
Where can you have a meal? You can have a meal "at" the restaurant or "in" the restaurant.
Where can you have a drink? You can have a drink "at" the bar or "in" the bar.
I would say 'in the restaurant' or 'in the cafe', because they are places that I enter, but 'at the bar' because I stand on one side and the barman serves me from the other.
Some people may say 'in the bar', using 'bar' to mean the whole room.