Somewhere in the Rockies, in the roughly 1,000 miles between Santa Fe, New Mexico, and the Canadian border, may be a treasure chest worth millions. The man who claims to have hidden the fortune back in 2010 is Forrest Fenn, now 87, a former Vietnam fighter pilot and art dealer. Fenn estimates that as many as 350,000 people have gone hunting for the treasure, he tells CNBC Make It, adding that there is no way of knowing whether anyone has actually gotten close. "It could be found soon or 1,000 years from now," he says. "No one knows where that treasure chest is but me," Fenn told NPR in 2016. That includes his wife. "If I die tomorrow, the knowledge of that location goes in the coffin with me." The main piece of guidance Fenn has offered is a cryptic 24-line poem he wrote in his self-published memoir, "The Thrill of the Chase." He has since shared the poem on Instagram. "Begin it where warm waters halt / and take it in the canyon down. / Not far, but too far to walk. / Put in below the home of Brown," reads one stanza.

"Read the clues in my poem over and over and study maps of the Rocky Mountains," Fenn recently told Business Insider. "Try to marry the two. The treasure is out there waiting for the person who can make all the lines cross in the right spot." The chest is nearly a square foot in size and weighs 40 pounds when full. It supposedly contains emeralds, rubies, gold coins and diamonds — all artifacts that Fenn, a self-taught archaeologist, amassed during his own sometimes controversial explorations in the Southwest, reports Vox. The millionaire was criticized in the 1990s for excavating the San Lazaro Pueblo Indian site he bought, for example, and the FBI searched his home in 2009 in connection with the sale of artifacts looted from the Four Corners area, though no charges were filed. Fenn originally filled the chest after he was diagnosed with cancer in 1988. He planned to drag it into the mountains to die beside it. After he survived, he left it in a walk-in vault at his house for years, where a couple of witnesses confirmed to NPR that they saw it filled to the brim with valuables. He decided to hide it and launch the hunt years later, during the Great Recession. "Lots of people [were] losing their job, despair was written all over the headlines, and I just wanted to give some people hope," he told ABC News.

Afternoon reflections of Bear tooth Butte in the calm waters of Bear tooth Lake in the Shoshone National Forest in Wyoming along the scenic Bear tooth Highway, The Bear tooth Mountains are located nor Education Images | Getty Images

Some of the Fenn treasure hunters are obsessive. "Most of my 12 hours every night I'm on Google or something looking up clues," Ricky Idlett, a steamboat operator in Mississippi, told Vox. "Every night. Every night I'm looking." There are a number of online forums where enthusiasts trade theories about where the treasure might be, including an entire subreddit called r/FindingFennsGold that's devoted to the cause. Fenn says he gets 100 emails a day, reports the New York Times. On a few occasions, he has had to call the police after unwelcome visitors showed up at his house or threatened him. "This one guy called me," Fenn told ABC News. "He said, 'Tell me where the treasure is right now. I'm going to kill you.'" And for some, the quest has proven fatal. At least four people are believed to have died in accidents while searching. This led some to call for Fenn to end the hunt. He hasn't, but he has added a few additional clues on his blog to try to help people stay safe.

In this July 4, 2014 photo, Forrest Fenn poses at his Santa Fe, N.M., home. Luis Sanchez Saturno | Santa Fe New Mexican | AP