Heat with the Sun and Passive Cooling
Nothing can be more comfortable for body and mind than living in a good solar-heated house. I say "good", because proper design is crucial to the comfort of such a house. You may have gone into a solar house and felt stifled by the glaring heat, or perhaps you shivered from the lack of it. Good passive solar design will provide just enough sunlight into the rooms to be absorbed by the surrounding thermal mass (usually masonry materials), so that the heat will be given back into the room when the sun goes down. The thermal mass is a kind of "heat battery" that stores the warmth, absorbing it to keep the room from getting too hot during the day. Equally important to thermal mass is insulation (such as straw bales, crushed volcanic rock, or thermal shades) that will keep that heat inside. Thermal mass materials need to be insulated from the outside, or else they will just bleed that warmth right back out. A rock house might have tons of mass, but be uncomfortably cold because of this energy bleed. So a good solar design will utilize materials of the right type in the right places, blending thermal dynamics with utilitarian design.
Many of the same principles that work to heat living space will also serve to keep that place cool in hotter weather. Other passive cooling strategies include wind towers that catch breezes and direct them through a house, and simple evaporative cooling concepts.