Fira de Barcelona Gran Via
The biggest fair in town
Fairs and conventions too big for the Fira on Montjuïc tend to use this big one, designed by Pritzker prize-winning architect Toyo Ito (with a solar power system) out by the airport. There are good connections between the two Fira complexes for events that are so big they take both areas.
It's also the main night venue for the Sónar Festival in June.