Back before the internet, hikers only had one tool to explore Rocky Mountain National Park. They simply called it the Dannen book.

Even experts, the guides who led hikes at the YMCA of the Rockies, for instance, had a mantra: What Would Dannen Do? The book Kent Dannen wrote with Donna, his wife at the time, simply titled “Hiking Rocky Mountain National Park,” was the first comprehensive guide for traversing the national park when it was released in 1978.

“It was the Bible for hiking for many years,” said Lily Melton, who along with Jack Melton acted as the museum curators and historians for the YMCA of the Rockies.

It seems hard to imagine today, when a Google search for, say, “Lake of Glass” will give you dozens of hits on how to hike there. But the Dannen book made the vast world of the national park accessible to anyone with an urge to explore.

“There were places Jack and I wanted to go, and we weren’t sure how to get to them,” Lily Melton said. “There just wasn’t good trail information up until that point. But once it came out, there were people who came from all over the world who wanted to hike. It was THE book.”

It seems sadly ironic, then, that Kent Dannen’s body was discovered Jan. 23 a half-mile from his home near Allenspark, on his 26-acre plot of land, after an extensive three-day search. Family members requested the welfare check after they hadn’t heard from him since Jan. 16. The Boulder County Sheriff’s Office does not believe his death was suspicious, unless the Coroner’s Office finds something unusual.

He was likely hiking, said Debbie Lanham, a sister who lives in Estes Park, something he still did nearly every day even though he was 78. Lanham worried about him living alone on such a big, isolated piece of property, but it fit him, too. Dannen idolized John Muir, and it showed in the way he lived his life. Dannen never owned a TV, didn’t care much about clothes and would keep cars forever, as long as they worked. Nature; his dogs; his son, Patrick; and his church were what filled his soul.

“We kept trying to encourage him to downsize, but he would say, ‘I’m out here with nature,’” Lanham said. “He was happy where he was. He loved it.”

Lanham called him unique, even quirky, a description Dannen himself embraced, making note of it in one of his many books on hiking in the park. But he was hardly a recluse who holed up in the mountains. He loved giving presentations on the park for groups and the library, worked as a hikemaster himself for the YMCA and sang in his church, the Presbyterian Community Church of the Rockies in Estes Park. He helped develop a meditation trail for the church, a way to help people connect nature with God.

“He was that kind of guy, who liked to share knowledge, and he was huge into learning,” Lanham said. “Those were a joy for him.”

The Dannens grew up in St. Joseph, Mo., not exactly a mountainous state. But Kent probably was inspired to write the book based on the many family vacations his parents, Dwight and Mary, took to the YMCA of the Rockies. They went so often that they admitted they felt bad about not showing their kids the whole U.S. and suggested a trip to California, Lanham said, until the kids, including Kent, insisted that they wanted to go to the YMCA again. The Dannens embraced their second home after that, and became huge figures for the YMCA. Their father served as president of the board for many years, and so did Kent’s brother, Doug. Lanham’s husband, Curt, now serves.

The Dannen book has, of course, been supplanted, not just by the internet but by Lisa Foster, who, in 2013, released “Rocky Mountain National Park: The Complete Hiking Guide,” complete with full-color photos and detailed descriptions of even the most remote areas of the park. Gerry Roach also wrote a well-respected book, “Rocky Mountain National Park Hikes and Climbs” in 1988, though that was more for mountaineers than for hikers. But the Dannen book, the size of a jeans pocket so you can stash it in a daypack, remains in the minds of those who hiked the park in the 1980s.

“At the time, it was everything,” said Sybil Barnes, who worked as a local historian for the Estes Valley Library for 14 years in downtown Estes Park and had the Dannens give frequent presentations. “They were among the first of my generation who really got people to realize that there was a lot going on here, if you just looked around a little bit and didn’t stay inside.”

In his later years, Dannen raised Samoyed dogs for sled teams and enjoyed showing them as well, winning awards for both. He continued to update his seminal hiking guide: After the Front Range flood of 2013, he told Lanham he needed to release a new edition to reflect the changes the angry water made on the landscape. He still had three dogs, up until his last hike.

It’s difficult to speculate on what happened. Lanham said the cause of death was hypothermia, and he was found with a bump on his head. He may have slipped on an icy patch. She is sad her brother is gone, as are the rest of their family.

“But we said to each other, ‘Can you see Kent in a nursing home? Absolutely not’,” Lanham said. “Not that we want him gone, but he lived the life he loved until the end.”