Hunnia is an adoringly grungy, subterranean music bar in Budapest. Perhaps it's not the most inviting of places from the outside, but trust me, it's worth proceeding downstairs. Hunnia is best known for its live concerts on Friday and Saturday evenings, when A- and B-level Hungarian bands take over the tiny stage. Expect a packed venue, and a bohemian crowd of regulars in their 40s and 50s who sing along louder and more passionately as the night progresses (you can check Hunnia's concert schedule).
Many of the bands that perform at Hunnia were part of Budapest's alternative music scene during the later years of communism in the '70s and '80s. Today, some of them are still going strong, along with their shrinking, gray-haired, but loyal group of fans. If you're looking for a truly local experience and taste of the local music scene, this is it.
Also, note the irony that this by all means anti-establishment bar is located in the heart of Budapest's fancy financial district, almost right across the Central Bank's grand building.