Budapest is often referred to as the “Country of Festivals” due to the big summer hits. This actually does not depend on season, the capital offers treats all year round, from electronic music to art and food & drinks festivals.
One colorful point on map is Barba Negra, which I admire. Let me state an important fact based on my own experience. The event hall operates two locations depending on the season. In winter, the place is indoors, and as it gets warmer it moves to Barba Negra Track, which is located near the Danube. That is clearly indicated on the ticket and on the website.
It’s gonna be your place in winter if you are into live concerts in the alt/rock scene.
They highlight the top Hungarian bands, some classic, and if a top band is touring around they will do concerts here on a very reasonable price compared to other destinations. Make sure you check their schedule in advance and book. You have low chances entering without pre-purchased tickets. The summer terrace, however, is huge and convenient, with a great view to the city from the Buda side.
What makes me often come here for concerts is the enviroment. Easy to enter, safe and monitored, fairly priced drinks, no waiting time.
Going by public transport is just fine but I suggest to plan the route. After you’ve made it to the right tram stop, just follow the mass of locals going there, you won’t regret it!