Sala Sonora, in an industrial estate on the riverside (metro Astrabudua), is THE reference : Time Out sums it up as 'like taking the Bilbao metro and ending up in Bristol'. A reference sound system, Friday and Saturday, underground techno and house, Europe's best DJs.
Fever, over in Indautxu, plays the bigger format across 3 floors including one techno, a more mixed crowd. Sala Azkena, ~200 capacity, holds the local alternative underground, tied to the Basque scene. Let's be honest : Bilbao's club scene is more modest than Madrid's or Barcelona's, and Sonora carries it almost single-handed.