On a bone-cold morning in early January, two hikers set out to circle Walden Pond in Concord, Mass. Although the concrete-fronted beach was deserted, the hikers were not alone.

An ice fisherman perched on the pond in a red tent. Across the way, where Henry David Thoreau built a small wooden house in 1845, a bundled-up woman stood at what would have been his doorway, staring meditatively at the view. Later, she joined her two companions walking back toward the beach — on the ice, not the well-worn trail around the pond.

Even when the temperature dips into the single digits, Walden Pond State Reservation is rarely empty. Recreational visitors prefer summer, but pilgrims flock here year-round to the site of Thoreau's “Walden,” a book of simple philosophy and a sacred text for nature writers.

In fact, University of Connecticut Professor Robert M. Thorson — who has just written the first official guidebook to the pond — said winter is his favorite time to visit, “when the water is frozen but not snow-covered,” and he can stand at his favorite spot to view the star-shaped symmetry of the pond.

Thorson's “The Guide to Walden Pond,” produced in collaboration with the Walden Woods Project, will be released by Houghton Mifflin on March 13. In size and format, the book resembles a nature guide, but it is much more. Part armchair travelogue, part narrative journalism, it packs an incredible amount of information about Thoreau and the pond's geological, biological and botanical environment into its 272 pages.

The guide comes out at an auspicious time. Last summer marked the bicentennial of Thoreau's birth, an occasion marked by worldwide lectures, events, and intellectual inquiry. The Concord Museum recently wrapped an exhibit of Thoreau's journals, called "'This Ever New Self': Thoreau and His Journal," in cooperation with the Morgan Library & Museum of New York.

It seems this 19th-century naturalist and writer continues to have an impact on American life that cannot be exaggerated.

“He's not just another dead white male who's going to go away,” Thorson said, noting the revisionists who have criticized Thoreau for misogyny or speculated about his sexuality — all issues that the UConn professor dismisses as irrelevant.

“He's a model for sane behavior,” Thorson said, trying to sum up Thoreau's legacy. “The thing is, it's not about nature writing; it's about setting a good example. Voluntary simplicity is what it's called.”

Thoreau built his “simple house” in 1854, on land owned by Ralph Waldo Emerson. Constructed of pine cut down near the pond shore and wood salvaged from a laborer's shanty, it measured 15 by 10 feet — enough to comfortably hold a narrow bed, his famous three chairs (“one for solitude, two for friendship, three for society”), his green writing desk and, eventually, a hearth for cooking.

Thoreau was not a hermit, as some believe, but walked frequently into Concord along the tracks of the Fitchburg Railroad. Friends like William Ellery Channing and his sister Sophia were among his visitors. The sojourn at Walden of two years, two months, and two days was as much about writing “A Week on the Concord and Merrimack Rivers” as it was about getting away from it all.

Thorson salts his account with wonderful tidbits, including the night the house stood empty (because Thoreau was in jail for refusing to pay a poll tax, which he recounts in his essay “Civil Disobedience”) and that it once hosted a fugitive on the underground railroad.

The author's deep knowledge shines throughout the account. Thoreau, he insists, would have abhorred the dressed granite stones that were posted to mark the house site. He recounts Thoreau's extensive scientific examinations of Walden Pond's depth and hydrological properties. The naturalist understood that the pond was fed not by springs or rainfall but a large underground aquifer.

Since its famous squatter left, Walden Pond has been the focus of sometimes misguided management. Thorson notes its recreational history, including the Walden Lake Grove Excursion Park, which drew visitors to the western shore from 1866 to 1902. In 1955, attempts to pump out the pond, to lower its level for swimmers, proved completely ineffectual — as the gasoline pumps sucked out the water, more seeped in from below. And an ambitious plan to expand the beach in 1957 was met with an environmental outcry led by Connecticut's foremost nature writer, Edwin Way Teale.

A geologist by profession, Thorson writes about the pond's origins in clear, precise language. He is also the author of “Walden's Shore: Henry David Thoreau and Nineteenth Century Science,” “The Boatman: Henry David Thoreau’s River Years,” and “Stone by Stone: The Magnificent History in New England Stone Walls.”

He traces his introduction to Thoreau to the late 1960s, a time when many undergraduates were turning to his ideas on the environment, civil disobedience, and simplicity.

“Thoreau became for me a sort of model, and a quirky model,” Thorson said.

In 2002, when Thorson was writing “Stone by Stone,” he reread “Walden,” finding in it deeper layers than he had understood as a young college student. A few years later, he began team-teaching a course at UConn with Robert Gross, "Walden and the American Landscape."

Taking students on tours of the pond only deepened his interest. A connection with an editor led to an offer from Harvard University Press and the publication of his first book on Thoreau. It was his wife who suggested that his pond tours might make a great book.

Concerned about affordability, Thorson originally proposed it as black and white with about 60 illustrations. Houghton Mifflin, however, expanded it to 91 color illustrations and striking spot-color sidebars. The book is priced at $16.99 for the paperback and $26 for the hardcover.

While the book will be stocked at the Walden Pond State Reservation's gift shop, and it is set up as a walking tour, Thorson also had in mind the armchair reader who perhaps has visited the property in the past or wants to know more about Concord's most famous native son. Each chapter gives context about Thoreau's time on the pond as well as later changes to the property.

A book release party will take place March 15 at the Walden Woods Project's headquarters in Concord.

Thorson has come a long way since his first visit to the pond in 1985, with his wife and two young children, shortly after moving to Connecticut from Alaska. He is now a life member of the Thoreau Society. He was involved in the Concord Museum exhibit and received a special tour of it.

“It was potent,” he said. “I'm not really big on material things, but there was (Thoreau's) desk and there was his journal and they were together for the first time.”

Although he thinks Thoreau's legacy is as much in his extensive journal as it is in the classic text of “Walden,” there is no denying the allure of the kettle pond that America's first naturalist put on the map.

Ultimately, Thorson writes, thanks to Thoreau, “an ordinary pond became an extraordinary place.”