San Diego is sneakier than it looks. The beach weather and the laid-back reputation convince people this is a passive city, but the live music scene here is genuinely deep - a real ecosystem from 200-person dive bars to waterfront festivals, and almost everything in it punches above its weight.
North Park Is the Answer
The Casbah is a religion. It fits maybe 200 people, the back patio is where you'll end up at midnight talking to the bassist from the opener, and the walls are covered in enough stickers and history to keep you occupied between sets. Nirvana played here. The White Stripes played here. Basically every band you've ever loved played here when nobody had heard of them yet. The bartenders have seen everything and they're still enthusiastic about the show. That's the measure of a room.
Observatory North Park handles mid-size touring acts in a converted theater where the original bones make everything sound better than it should. Music Box is walking distance, and on a weekend night you can move between all three following your ears without calling a rideshare. That's North Park.
The Institutions
Belly Up Tavern in Solana Beach is the other pillar - slightly bigger, beach-town energy, tables in the back if you want them (you won't). The drive up the 5 from downtown is 25 minutes and completely worth it. SOMA handles the punk and metal side of things. Pechanga Arena and Viejas Arena at SDSU take the arena tours when they come through.
Festival Season
Every spring, CRSSD Festival takes over Waterfront Park with a stacked electronic and indie lineup against a downtown San Diego backdrop - the bay is literally right there, the weather is what you'd expect from San Diego in March, and the crowd brings actual energy. Pre-show in North Park: Cucina Urbana on University Ave for sit-down Italian, or Oscar's Mexican Seafood on the corner for the faster version. Find San Diego concert tickets on Evil Tickets and plan around the weather, which will be perfect.