While in Iceland a few weeks ago, I tried to work up the nerve to try hàkarl, one of the local delicacies. It is prepared by burying chunks of Greenland shark meat in the ground for a few weeks so that it can “ferment” (the nicest word possible here), after which it is unearthed and kept in a smokehouse until extra tasty. The smell goes on for miles. One tourist compared it to “a tramp’s socks soaked in urine.” The flavor, everyone says, is not nearly as bad as the aroma, although the description alone is sufficient to tickle the gag reflex.

My suspicion was that the hàkarl tradition began with one drunken Viking daring another to eat putrid seafood. On first arriving in Reykjavik, I felt up to the challenge, if only because clogged sinuses had deprived me of smell and taste for a week. But Iceland has the world’s cleanest air, and after breathing it for a couple of days, my senses were functional, even keen … and I flinched. My wife was unable to contribute to the YouTube subgenre of “tourist eats hàkarl” videos. Clearly no Viking blood flows in these veins.

Be that as it may, I could tell, by the time we left, that the city itself had a smell -- distinctive and unpleasant, like rotting eggs perhaps. It came from the sulfurous fumes emitted by Iceland’s geothermal springs. The island sits atop (or rather, was created by) the ridge or boundary between the North American and Eurasian tectonic plates. As they move apart from each other, heat surges up from beneath the earth’s crust – hence the volcanoes, and frequent minor earthquakes, as well as water so hot you can boil an egg in it.

Returning to my desk a few days later, I found, atop the clutter, a book showing the glowing mouth of a volcano on its cover, with the title Why Hell Stinks of Sulfur: Mythology and Geology of the Underworld by Salomon Kroonenberg (Reaktion Books, distributed by the University of Chicago Press). The topic had sounded intriguing before our trip. Now the title itself promised to keep the vacation mood alive just a little while longer.

Kroonenberg is emeritus professor of geology at the University of Delft, in the Netherlands – and Why Hell Stinks of Sulfur seems very much a professor emeritus’s book. It blurs the line between memoir (or travelogue) and a pedagogically compelling exposition of the author’s field. And the author wanders across that field guided by his own sui generis map. As far as I know, “the underworld” is not a contemporary geological concept. It leads him across an enormous and various range of ancient and modern literature concerning the world beneath our feet. The earth sciences become part of the humanities, and vice versa. The treatment is essayistic (comparisons to Stephen Jay Gould come to mind occasionally) yet the volume coheres as a whole. It is the work of someone who knows not only his subject but the history and sources of his own mind. This might be called full intellectual maturity, a ripening; the quality is rare.

Kroonenberg’s point of departure is the contrast between the crystalline transparency of the heavens above -- where we can see objects billions of miles away, weather permitting – and the opaque universe beneath our feet: “the most unknown part of our planet, despite the fact that the center of the Earth is no further away than London is from Chicago.” The deepest location most of us will occupy for very long is six feet under, and not out of curiosity. The association of the underworld with darkness and death comes naturally, and the heroes who travel in its realms (Orpheus, Anaes, Dante, etc.) usually go there because they’ve lost someone. In the case of Jesus – according to the pseudepigraphal Gospel of Nicodemus – the trip is a mission to subdue Satan and lead “Adam and all the saints out of hell.”

Following the geographical references and descriptions in these and other accounts of subterranean visits, Kroonenberg goes in search of the real-world sources of how the underworld has been depicted – the original river that becomes mythologized as Styx, for example. Kroonenberg is often pursuing suggestions left by explorers and scholars over the centuries. Their lives and writings become part of the narrative, along with the author’s own travels and his explanations of geological phenomena.

The author moves through history in a crablike fashion -- from ancient and medieval stories to recent knowledge of the earth’s structure, but never through the shortest possible route of compare-and-contrast exposition. Alongside the fictional or legendary figures, more and more historical figures appear as the chapters proceed, bringing their speculations on stage. (Leonardo da Vinci drew a reasonably good cross-section of the Earth, showing the layers beneath its crust. René Descartes “was the first to assume that the core of the Earth was hot.”)

All the while, Kroonenberg’s personal recollections weave in and out of the text, from his childhood scientific interests to aspects his career, such a collaborating with specialists in pedology, the study of dirt, while working at an agricultural school:

“Experienced soil surveyors roll a small clump of soil into a sausage and stick it into their mouths, chew it, ponder it for a while, and then pronounce their verdict: light loam, 15 percent clay. And then it starts, as there is always more than one pedologist around the pit at any one time. They take turns to jump in, pick at the wall, and taste the soil: ‘I think it’s heavy loam, 20 percent clay.’ … There are endless discussions on the basis of qualitative, subjective observations, where the lack of statistical evidence is compensated for by years of experience in hundreds of pits. Bullshit around the pit, that’s what we call it.”

Not surprisingly, one of the author’s favorite books as a child was Journey to the Center of the Earth, by Jules Verne, in which the narrator and his uncle, Professor Lidenbrock, gain access to the subterranean world through a volcano in Iceland. Kroonenberg recalls that the uncle was “an irritable and conceited scholar who gave a not particularly popular course on mineralogy” and gathered knowledge “for himself and not for others.”

In the Scholastic Books edition of Verne’s novel that I read constantly as a kid, that little bit of characterization was left out. Perhaps the editors worried that it was too unflattering a picture of a teacher. In any case, Kroonenberg himself is nothing like the uncle, if his book is anything to go by. It makes me want to go back to Iceland to have a look at that volcano. Next time, I might also sample a bit of hàkarl, or, failing that, chew some dirt.