If Swedish massage is about relaxing, deep tissue massage is about actually fixing something. It's slower, more deliberate, and a lot firmer, working through the layers of muscle and the connective tissue underneath (fascia, if you want the technical term) instead of just gliding over the top.
Most people book a deep tissue session because something specific is bothering them: a stiff lower back from sitting all day, shoulders that never seem to loosen up, or muscles still holding tension from an old injury or a hard training block. The therapist will usually lean into it with their elbows, forearms, or knuckles, pressing along the direction of the muscle to work out the knots and adhesions that have built up over time.
It's not always a comfortable experience. There's real pressure involved, and you might feel some soreness the next day, a bit like after a good workout. That's normal. What it shouldn't feel like is sharp or unbearable pain. A good therapist will check in and adjust based on what you can handle.
It's not for everyone though. If you've had recent surgery, you're dealing with a clotting disorder, or you're pregnant, skip it or check with your doctor and a qualified therapist first. The pressure is too intense for those situations.
Most sessions run 60 to 90 minutes, and it's common to focus on one or two problem areas rather than doing a full body treatment.