Jon Sinclair has a confession to make: after 15 years of professional racing, Bloomsday was always his favorite. Now, the two-time champion is coming back to celebrate the race's golden anniversary—and he's traded his running shoes for climbing gear.

Sinclair, now 68 and living in Lafayette, Colorado, dominated the men's elite field in the 1980s. He won the Bloomsday championship in 1983 and 1986, and finished as runner-up in 1981 and 1982. His secret? He loved hills. The 7.46-mile course is no flat stroll—it winds from downtown Riverside Avenue, climbs toward Spokane Community College, tackles the infamous Doomsday Hill, drops down Broadway Avenue, and finishes at the north end of Monroe Street bridge.

"Doomsday Hill is the toughest part of the race for everybody. But it favored me," Sinclair explains. "I was always better at 10,000 meters up to the half marathon. That was always the kind of racing I loved."

These days, Sinclair doesn't run much. He'll jog 2 or 3 miles every other day, but his real passion is rock climbing—three to four times a week, year-round. "I don't have any cartilage underneath my kneecaps anymore," he says with a laugh. "I have about 120,000 miles on my legs. If you figure my stride length was about 3½ feet, my feet hit the ground more than nine million times. It speaks to the human body to be able to withstand that kind of thing."

Sinclair is among several Bloomsday legends invited back for the 50th running of the event this Sunday. His wife, former elite winner Kim Jones, plans to run ceremoniously. Sinclair will likely mingle in the crowd. The couple ran their final competitive Bloomsday races in 2003, married three months later, and will celebrate their 23rd anniversary this August.

"I've been really fortunate because most of the people I've run against aren't running at all anymore," Sinclair says. "They've had knee replacements or whatever. I still have all the original equipment."

Rock climbing doesn't punish his body the way running did, but it delivers the same thrill. "For people that climb, they see it. For people that don't climb, they can't understand it at all," he says. "It's really challenging in a way that running isn't."

Still, for a man who made a living conquering hilly courses—and who knows every rise of Cemetery Hill and every punishing step of Doomsday—returning to Bloomsday for its 50th race feels like coming home. And that's a journey worth celebrating, whether you're running it or not.