I was out for a trail run tonight, and it was one of those neat nights where it was drizzling and cloudy. It occurred to me during the run that running on a trail is about the polar opposite of regular treadmill "cardio".
On the trail, the surface is uneven and natural. There are varying hills and declines. You are surrounded by nature and all its sensory input.
Trail running also makes stopping and starting more natural I believe. I mixed up walking, running, and breaks where I would squat, over the course of about an hour tonight.
It was a great experience, as "workout" isn't the right word to describe a trail run.