High intensity interval training (HIIT). If you can keep it up for more than 10 to 15 minutes you’re not doing it right.
Or else it’s just a technique for getting somewhere quicker than by walking that Baden Powell invented for the Scouts. 😉
However, the debate still rages as to whether long steady state or HIIT is better for fat loss. If you’ve got the time, do HIIT on some days and walk for an hour on other days. Preferably non-training days but if you must do HIIT on training days do it at the end of training.
Walking should be done as fast as you can with out running. Walking at speed is inefficient (that’s why we run) and inefficient is good for burning calories.