I find that using public transport (walking to train stations, bus stops, etc) instead of driving, doing all my own cleaning/laundry/cooking and doing 10 pull-ups whenever I walk under my pullup bar (which is in my bedroom door frame) is enough to keep me fit, but when I have the time I make sure to swim laps and go for a stroll as well. I rarely attend the gym, but if I have to work out, I do it at a place called BodyTec - they attach electrodes to my skin that makes my muscles rapidly expand and contract while I work out, intensifying my routine. Typically a 20 minute session provides the same benefit as a week's worth of gyming. I was skeptical at first but the results have been pretty consistent.