I'd been thinking about parks for a while now. I live in Toronto and I'm fortunate to live between two terrific trail systems that are popular with cyclists, walkers, picnickers and a whole bunch of other people.
To start with - in the warmer months its cheap fitness. You can walk or run, cycle or play Frisbee in a very comfortable environment. There will be plenty of benches and picnic tables along the way if you want to do some push-ups with elevated legs or triceps dips or lunges. You'll probably find that your workout lasts a lot longer because you're enjoying being outside.
But there is something so special about a woodland trail - especially when you're in the big city. It feels luxurious. You've got a babbling stream with bridges that cross back and forth over it every couple of hundred feet. There are ducks to watch and squirrels to feed. Its almost like visiting the cottage - but its free!
The crowd changes depending on the day of the week. Go on a Sunday afternoon and you'll find huge extended families with ten coolers grilling under the shade of an expansive willow tree. Go during the week and you'll find seniors doing an aggressive powerwalk. You'll also see the dogwalkers with their deluxe red leashes trying to keep all five dogs from jumping in the stream at once.
So, go and visit a park, and enjoy a little natural serenity.