The above along with a good cardio program is a great way to expend more calories than you are taking in which is the key formula for fat burning and weight loss.

These days, I do go to gym, but over the weekends, I do rock climbing. This is maybe one of the best ways to lose weight I've come across. Its loads of fun, you meet really great people and the movements are all natural. Also, its a complete body workout. Because your having fun and challenging yourself on the rock, you don't really realise how much of a workout you're getting, until the next day

Increasing muscle mass is an effective way to increase metabolism and like you say, you don't need to pump iron every day or have bulging biceps to achieve this. Walking and swimming are just two ways to keep in shape and help keep those muscles active.