How to make a Dakota fire hole - photo

[neilbourjaily]

Rocket Stove without the shearing, plasma or bandsaw cutting steel and welding, nor the portable aspect.

This appears to be a survivalist image.
Beyond that, however, it has to do with accessibility. Consider the most accessible form of energy, other than solar, is steam. All one needs is a fire and a container. Make it more sophisticated, and the steam can be contained and used to drive a piston, an arm, a shaft, etc. This 'Dakota Fire Hole' is an accessible rocket stove, and the design predates.