A local himself, he says the suburb is a perfect fit for the new cafe.
"This area's so multicultural, there's an urban rawness.
"It's not gentrified. I like that you can walk down the street and buy taro."
There's a large open kitchen along the back wall, an inside bike rack and an exposed roastery where customers can sit and watch it all happening.
Mr Murphy is eager to show us around - and not just the new parts. He makes his way towards the back entrance of the premises. Beyond the kitchen, we are confronted by an old dumbwaiter and, to the right of this, a dizzying spiral staircase that curls away into the darkness.
This was the entrance to a storage room into which heavy sacks of mail were hoisted via the dumbwaiter.
But it's not the strangest find, points out Mr Murphy, leading us outside to an imposing door.
"We had to get New Zealand Post to arrange a locksmith because no one had a key," he explains as we follow him inside, along a low, curving corridor of thick concrete that expands out to a large underground room.
"No one had been in this room for 15 years," he says. "There were cobwebs everywhere, old documents, a woman's woollen green gown from the 70s, and bikes still hanging."
He pushes open a resistant little window to reveal an odd external space where pigeons roost. Except for the window, the room is unnaturally lit and silent, save for the pigeons' guttural warbles and furious beating of wings that echo up the barrel of space.
The concrete walls are partially canvas, with half a dozen initials and dates one could surmise belong to post office workers past. Scrawled on a white beam is an indecipherable signature above a more legible "9:45 AM, Sat 9th May, 1959."
On the far wall: "R. Bach, 1958" and in fat black spray paint: "H.K 1976."
"That's the year I was born," says Mr Murphy, who is puzzled as to why the room was left locked for so many years, with people's belongings still inside.
"It's just kind of random ... randomly cool," he says, looking around before being interrupted by his phone ringing.
"I'm in the dungeon," he tells his caller.
Memories of a worker
Former post office typist and machinist Marjorie Vermeulen worked at the Grey Lynn branch from 1969 to 1991. She remembers the basement. "I remember going down there. It was used for storing documents. "
Mrs Vermeulen, who still stores a postie's bike outside her house, is pleased to learn of the new cafe in the location of her old workplace.
"I think it's a lovely idea. When I first heard the post office was closing, I was quite heartbroken because it was such a lively place. The people who worked there were happy in their jobs, we were a team."
New Zealand Post spokesman Michael Tull confirms the room was used for storage and clearly hadn't been cleaned out for some time.
"As to why it was locked, the answer almost certainly lies in the human tendency to look at a messy room filled with all sorts of junk, contemplate cleaning it, then decide that 'out of sight is out of mind', especially since the basement room wasn't required for any other purpose."
Mr Murphy says some of that "junk" is very much in sight in Kokako, which opened yesterday. An old set of scales and the 'open' sign will reflect some of the building's history - in a cafe aiming to stamp its mark.
