All these other subjects notwithstanding, it was Kircher’s theory about the interior of the earth that captured, or at least deserved, the most attention. As he explained, “the whole Earth is not solid but everywhere gaping, and hollowed with empty rooms and spaces, and hidden burrows.” Deep down, it holds many great oceans and fires, interconnected by a system of passageways that reached all the way to its core. In his view, volcanoes, however awful and awe-inspiring, “are nothing but the vent-holes, or breath-pipes of Nature,” and earthquakes are merely the “proper effects of subterrestrial cumbustions” that are sure to go on constantly. The “prodigious volcanoes and fire-vomiting mountains visible in the external surface of the earth do sufficiently demonstrate it to be full of invisible and underground fires,” he wrote. “For wherever there is a volcano, there also is a conservatory or storehouse of fire under it.... And these fires argue for deeper treasuries and storehouses of fire, in the very heart and inward bowels of the Earth.”