Don’t feel guilty walking away from your desk. In fact, quite the opposite: Studies have shown that taking short breaks can help you do your job better. It's in your (and your employer's) best interest to take a break and going one step further, going outside the building, has also been shown to reduce stress levels and make you happier.
Sitting in the same place all day, like behind your computer, can leave you uninspired, while walking outside provides additional stimulation and enhances creativity.