Forget pricey rafting trips. We mean getting back to the basics: hiking, cycling, swimming—all butt-kicking leisure activities you can enjoy for next to nothing.

Want to see serious results? “Add sprint intervals” says Sara Celik, a naturopathic doctor and fitness trainer. “Go on a hike with friends and at random intervals yell out ‘Challenge!’ This is the signal for everyone to sprint for 45 seconds. Continue this throughout the hike,” says Celik.

Result:  “The caloric expenditure from a nice, long hike at a leisurely pace, and the intensity kick that comes with short bursts of intense effort,” says Celik. Switch up the pace when cycling or swimming, too.