"The gym is big and empty now."
Translation:Sala de sport este mare și goală acum.
In Romanian usually "the gym" is translated as "sala", so I think that using just "sala" should be accepted as a correct response. Ex: "I'm going to the gym" in most cases will be "Merg la sala" and not the full version "Merg la sala de sport".
It's true that "sala de sport" is more precise, but it's rarely used :)
Languages evolve everywhere. 20 years ago if someone said "merg la sală" the immediate answer would have been "la care sală ?" There were few gyms owned by the schools and no common habit to go to the gym as a way of life, as today. So generally use "sală de sport " unless you are having a friendly chat.