This night-club is located in Solana Beach, just a few miles north of San Diego proper. It's situated on a somewhat trendy street of hipster furniture and designer knick-knacks, and some of that gets reflected in the crowd that comes in to party. By this I mean that the Belly Up tends to pull an older, well-groomed crowd. Piercings are few and far between.
The tavern at a glance resembles a converted warehouse, although it is apparently a World War II-era wooden Quonset hut. As usual, its large stage plays out to a large dance-floor; here's where things get interesting: in addition to a raised seating-area in the back, there's also another to the side facing the stage. It actually gives you an opportunity to practically get right behind the musicians on stage. There's a smoking area behind the building. Just go through the exit to the left of the stage.
The musical fare is basically folk and reggae, with occasional excursions into experimental rock (e.g. Frank Black, Blonde Redhead). Cover charges tend to oscillate around $15, although local acts can go for cheaper. Although there is no food served in the club, there is a good pizza joint nearby.