Calories burned: A moderately paced walk (3 mph) carrying a light load (<25 lbs.) burns 5 calories per minute.
The Work: In the old days in rural areas, leaving the house to buy some seeds or visit the neighbors clearly meant walking at least five miles to get to the intended destination. Walking was just a part of life, long before it became a nuisance that only city people at the mercy of public transportation have to keep doing.
Accessibility: Very high. If it’s at least somewhat nice out, it’s good to break up the constant interaction with computers, TV and chairs to get out into the world. It’s also a good middle ground between physically idle activity and pushing yourself to the limit during workouts.