I have pondered the purpose of these several times. They clearly relate back to the technology used to form megalithic structures we see around the world, likely involved softened stone. One in your picture shows stress cracks above/below the entry like the stone did this as it cooled back to normal. Are they permanent domiciles, hunting cabins, cages, places to meditate that harness energies emitted by the stones, or? I haven’t seen any with smoke holes, so occupying them in cold temps seems problematic (climate changed?). Are the holes sized for occupant entry but too small for large predators to get through? It would be interesting times to build / use these where technology to soften stone was available / portable but the earth was wild enough to need shelter from big predators. Or are they places to ‘keep’ specimen creatures they didn’t wish to kill but were too dangerous to let run wild?