This copperplate engraving from the ‘Mundus Subterraneous’ demonstrates how all bodies of water on the surface of the earth are interconnected through subterranean channels. As 

 explains: 'the whole Earth is not solid but everywhere gaping, and hollowed with empty rooms and spaces, and hidden burrows'. The map shows how vast oceanic whirlpools feed these channels, while mountain springs derive water from the same internal resources, creating a cycle of water above and below ground. At the centre of the Earth, a large ball of fire heats these various reservoirs and forces water to the surface by convection through an interconnected hydrological labyrinth. Kircher’s vulcanology is further expressed in a second engraving ‘Systema Ideale Pyrophylaciorum Subterraneorum’, which shows how magma moves though similar subterranean passages. 

This fantastical image, a cross-section of the earth, was published in 

’s ‘Mundus Subterraneous’ ('Subterranean World', 1665), his extraordinary encyclopaedia of subterranean geography, in which he illustrates his theories of how the three elements – water, air, and fire – flow through a system of channels before reaching the Earth’s surface. As such it is one of the earliest works on speleology.

On a visit to Sicily in 1637–1638, Kircher had been greatly affected by witnessing the eruption of Mounts Aetna and Stromboli, and his own terrifying descent into the crater of Vesuvius. As a Jesuit, Kircher rejected, for Scriptural reasons, the Cartesian notion of a slowly evolving earth, but he nevertheless displayed a great interest in the internal structure of the globe. He suggested that the earth had a central fiery region that was connected to the crust at many points and that the Earth also contained vast reservoirs of water. When the water and fire interacted, earthquakes, volcanoes, springs, and storms were the result.

For centuries scholars had speculated on how the world was made. Advances in cartography which, by the mid-seventeenth century, were describing and illustrating the Earth’s surface with increasing scientific precision, had growing influence on this ancient debate. Leading thinkers, like 

, were simultaneously studying natural sciences, medicine, philosophy, and religion in new light and attempting to combine their findings with pre-existing theological concepts. 

The inspiration for the ‘Mundus Subterraneus’, from which this map derived, was Kircher’s visit to Sicily in 1637–1638, where he witnessed an eruption of Aetna and Stromboli. He prefaced the work with his own narrative of the trip, including his spectacular descent into Vesuvius, 'I thought I beheld the habitation of Hell, wherein there seemed to be nothing besides the horrid phantasms and apparitions of Devils'. He heard 'horrible bellowings and roarings' and there was 'an inexpressible stink'. His observations of these volcanoes led him to conclude that the centre of the earth is a massive internal fire for which the volcanoes are mere safety valves.

Kircher rejected for Scriptural reasons the Cartesian notion of a slowly evolving Earth, but he nevertheless displayed a great interest in the internal structure of the globe. Although Kircher was an ardent collector of fossils and amassed a sizable collection for his ‘Musuem Kircherianum’ at the Collegio Romano, one of the first public museums. He did not see them as evidence of changing ocean levels or geological catastrophes but simply as signs and marvels of the Creation.

’s arresting image, water literally boils to the surface of the Earth via a system of subterranean channels, heated by a central inferno.

Kircher’s Watery World View