Get off the pavement
Take advantage of the varied terrain nature has to offer. While most cardio machines will only let you go forward and up, outside you can also tackle downhills, test your lateral movement skills and more. "Try boulder bounding up dry riverbeds, then "slaloming" downhill through the trees," says Tina Vindum, founder of OutdoorFitness.com in Marin County, California. "I combined that with body-weight exercises using logs, boulders, tree limbs."
Look for props
Even if you don't have access to hiking trails or a body of water, it's usually easy to find a park or playground. Vindum suggests using benches for dips and push-ups. Think monkey bars are only for kids? They're also good for stretching and practicing pull-ups. Put your legs to work doing step-ups and calve raises on curbs.