Man has been walking since thousand’s of years, but only in the last 100 years or so man has started walking on flat roads. The primitive man walked a lot, but he walked mountains, deserts and valleys.
Today I got sick of walking on a flat surface, so I jumped walls, walked over tree embankments. It felt like I was doing much milder version of Parkour. I immediately built up some sweat, which impossible just walking in this december evening weather.
Do try not to walk on straight roads, find a road which is steep. Try to find something you can climb or jump on during your walk. It is way too fun.