Plutarch De primo frigido 20

[20] To go no farther, what means our own yearly practice to alter our lodgings and habitations, while we remove in the winter so far as we can into the upper parts of our buildings, but in the summer descend again and seek convenient refuge in the lower edifices, sometimes enjoying ourselves under ground in the very arms of the earth? Do we not do it, as being guided by our senses for coolness’s sake to the earth, and thereby acknowledging that to be the seat of primitive cold? And certainly our coveting to live near the sea in winter may be thought to be a kind of flight from the earth, since we seem to forsake it, as far as we can, by reason of the nipping frosts, and run to encircle themselves with the air of the sea for warmth’s sake; and then again in the summer, by reason of the scorching heat, we desire the earth-born upland air, not because it is cold of itself, but because it had its original and blossomed from the primitive natural cold, and is imbued with that power which is in the earth, as iron is imbued with the virtue of the water wherein it is quenched. Then again, of river waters we find those are the coldest that flow upon gravel and stones and fall down from mountains; and of well-waters, those which are in the deepest wells. For with these the exterior air is no longer mixed, by reason of the depth of the wells, and the other arise out of the pure and unmixed earth; like the river that falls from the mountain Taenarum, which they call the water of Styx, rising out of a rock with a parsimonious spring, but so cold that no other vessel except the hoof of an ass will hold it; for all other sorts of vessels it breaks and cracks to pieces.