Greg Brick's tour of the dark caverns and damp passageways of the Twin Cities underground isn't for claustrophobic readers. Nor is it for those too squeamish to relish Brick's frequent immersions in raw sewage, his encounters with fetid air and sulfurous smells, and his meditations on the origins of the gelatinous "sewer slime" that coats the walls of St. Paul brewery cellars.

For the rest of us, though, "Subterranean Twin Cities" is an enjoyable plunge, sprinkled with fascinating historical side trips, into a netherworld that sane people wouldn't want to make a destination -- and shouldn't.

For there's danger in the caves, sewers and tunnels through which Brick crawls as he identifies Twin Cities sedimentary formations, city sanitation relics of eras past, and examples of engineering derring-do. A geologist, former public works employee and longtime speleologist, he repeatedly evokes the sudden rainfalls that can turn a trickle of wastewater into an underground torrent that leaves no breathing room at the top of the sewage passage. He also endures recurring bouts of what he calls "Rinker's Revenge" -- a fierce intestinal disorder, named after a city engineer of the past, that follows Brick's every expedition into the sewage of the north Minneapolis Tunnel.

Such risk-taking requires powerful motivation. Why does Brick -- who has previously authored "Iowa Underground" -- apply his energies to seeking out Schiek's Cave far beneath downtown Minneapolis and exploring the subterranean fungal harvesting grounds of St. Paul's abandoned Mushroom Valley? What compels him to advance through sewer muck so high it stains his shoulders, so thick it sucks off his shoes? What fun Freud would have with Brick's obsessive burrowing into the ground!

But there's no self-analysis here. Brick offers few clues of the sources of his passion for the underground beyond tidbits of his employment history and passages that attest to his fascination with geology and Twin Cities history.

Instead, he gives us vicarious glimpses of surprisingly lovely images we will never see: the flickering shadows his candle casts on the sandbanks of St. Paul's Fountain Cave; an abandoned milk truck, entombed for the ages, that he discovers in another St. Paul cave; the entwined earthworms that "covered the floor like spaghetti" at the bottom of Schiek's Cave, and the view from 75 feet underground to the streets of Minneapolis, "light streaming through the hexagonal lid far above us."

Good books are supposed to transport us, even to places we think we don't want to visit. Despite his occasional use of labyrinthine sentences and unfamiliar geologic terms, Brick leads us to the buried guts of our cities and brings us back wanting more.

Jack El-Hai is the author of "The Lobotomist: A Maverick Medical Genius and His Tragic Quest to Rid the World of Mental Illness." He lives in Minneapolis.