When some types of athletes need to drop weight, one of the strategies they do is to walk at a normal-brisk pace for hours until they hit a certain number of estimated calories burned. The reason they walk is that it has a much lower risk of injury and puts less stress on the body than most other forms of cardio exercise (perhaps excepting a stationary bike) and our bodies are good at naturally finding a pace we can sustain ~indefinitely.

It feels like a bit of a hack when you go for a 2hr walk and end up burning almost 800kcal listening to music, talking to people on the phone, maybe taking care of chores like paying bills.