Why do caves stay cool year-round?

A cave’s temperature is controlled mainly by the average annual temperature of the region rather than daily hot and cold spells. Thick rock acts as insulation, and deep interior spaces are shielded from sunlight and wind. In many caves, the temperature remains nearly constant all year with only slight seasonal variation. Water seeping in from above can also help regulate conditions. That stability is why caves often feel cool in summer and relatively warm in winter compared with the surface.