Endurance comes naturally to humans as that is how we are built.   Our bodies are built to walk about 10 to 13 miles per day and go for days without food and still able to survive.  Under 70% max heart rate our bodies use fat for fuel for activities like walking.  We can use our stored fat very efficiently which makes it difficult to get rid of when we have too much.  In our modern lifestyle, we tend to overeat and under exercise which leads to being overweight.

In the photo below my wife and I hiked to the top of Mount Corcovado in Rio De Janeiro back in 2016.  It took an hour and a half hiking up steep and dangerous terrain.   Every step was like stepping up 4 stairs so I thought about doing steps ups for 90 minutes, it was very difficult but rewarding.  Everyone else took the trolley, but we signed our lives away on waiver and went for the hike, lol.  It was 90 degrees, humid and I ate a giant omelet immediately before, I urge you not to eat eggs or meat in general before a hike.  I was cramping the whole way up and the wife was making fun of me because I ate my omelet and half of hers.