"I thought 'if he could do it, so could I'."
In July, Sinclair - who stands 2.31m tall - set a goal of climbing Mauao 50 times. Despite busted legs from old injuries, he achieved this in September - and has not stopped. This Sunday's 300th climb will, in reality, be closer to 600 after he developed a habit of climbing Mauao twice each time.
"I go up the 4WD track and then down the stairs, then turn around and go up the stairs and down the 4WD track."
Sinclair said the climbs have transformed him. Not only has the gentle giant lost nearly 40kg, he loves life again.
"When I get to the top, I don't know what it is ... when I hear the birds singing and I hear those waves on the other side, it's just so nice. It's unreal. It's like its own magic up there."
Sinclair said he wanted to share his story to help anyone else who might, like him, be struggling with depression. He had a message: "Don't let things hold you back like I used to."
"I'd hate to think what I would be doing if it wasn't for the walking."
Each year one in five Kiwis are diagnosed with a common mental illness or addiction.
A government inquiry into mental health and addiction found increasing numbers of children suffering and self-harming. The inquiry also reported that New Zealand's 2017/18 suicide rate was the highest since 1999, with 525 people ending their life by suicide and another 20,000 attempting to do so.
Mental Health Foundation of New Zealand chief executive Shaun Robinson said being active was an important step to wellbeing and it was something the foundation advised as part of a Five Ways to Wellbeing formula.
If someone could combine activity with time spent in nature, "all the better".
"Research shows that even small amounts of time connecting to the natural environment boosts mental health. We never know what life challenges lie around the corner, but if we invest in our mental health we are much better equipped to handle tough times and can prevent mental health issues."
A report released in February by Mental Health Commissioner Kevin Allan estimated nearly half of New Zealanders would live with mental illness and/or addiction at some point during their lifetime.
The report also found one in five New Zealanders lived with mental illness and/or addiction each year. Nearly 5 per cent would be considered to have a severe mental health and/or addiction condition, 9 per cent a moderate condition, and 7 per cent a mild condition.
Allan said access to mental health and addiction services had grown to 73 per cent over the past decade, but funding had only grown 40 per cent.
Help is available
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call police immediately on 111. Or if you need to talk to someone else:
Need to talk? Free call or text 1737 any time for support from a trained counsellor
Lifeline: 0800 543 354 (0800 LIFELINE) or free text 4357 (HELP)
Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO)
Healthline: 0800 611 116
Samaritans: 0800 726 666
Youthline: 0800 376 633. Kidsline: 0800 543 754 (available 24/7)
Whatsup: 0800 942 8787 (Mon-Fri 1pm to 10pm, Sat-Sun 3pm-10pm)
Depression helpline: 0800 111 757 (available 24/7)
Rainbow Youth: (09) 376 4155.