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Mr Horne (43) is running up the world's steepest residential street, Dunedin's Baldwin St, 126 times.
''It's a real grind. At 6am, it's cold and dark. There's not a lot of stimulation, so you grind up and down.''
He does about 10 ascents every second day, which takes him just over an hour.
It is a challenge he admits doing for purely financial reasons - to raise funds for the Otago-Southland Division of the Cancer Society alongside next Friday's Daffodil Day collection.
As a member of the Otago/Southland Cancer Society board and chairman of its audit, finance and risk committee, Mr Horne, who is a partner at accounting firm Deloitte, is well aware of the financial challenges facing the society, which does not get any government funding.
So when Cancer Society Dunedin marketing manager Mark Hamer came up with the Everest challenge, suggesting a team from the charity's Dunedin branch should lead by example during the national ''Choose your Challenge'' fundraiser this month, it was suggested Mr Horne give it a go.
''It seemed like a good idea at 5.30 on a Thursday night ... but by Friday morning ...''
His wife, Katrina, was also taking part, completing 75 ascents to date.
They hoped to raise about $4000 by the end of the month. Seven people in the Dunedin branch were taking part in the challenge, including the mastermind of the scheme.
Mr Hamer said he had managed 25 ascents so far, admitting the challenge was ''very tough on the knees''.
''We're way past base camp now.''
The idea behind it was that people with cancer faced an impossibly steep climb in their life, as climbing Everest would be.
So far, the team had raised $1210 and hoped to reach its target of $1500.
Details of the challenge can be found on the society's website.