'I used to be a graffiti artist. What you'd call a vandal."
It's a bold statement from guide David Russell, especially as he's talking to a bunch of street art admirers who've signed up to Melbourne Street Art Tours' expedition through paint-strewn alleys.
"At the end of the day, it's just a piece of paint," he continues. "The only reason you think it's vandalism is because you've been told that."
The fast-talking artist-turned-photographer has a point. However, it's hard to entirely concentrate on his words while we're gazing from a multilevel car park near Federation Square at the colourful brick wall opposite.
High above a sea of tags is a vast painting of a fruit bat, its head emerging from an abstract structure of green and white. It's a magnificent piece of art, at least 10 metres high, and Russell says it was an officially authorised production which would have taken 30 hours' work.
Because it's so high above ground level, the fruit bat is unlikely to be painted over by other street artists; but that also means it can only be seen from this car park.
That, in a nutshell, is Melbourne's famous street art scene: balanced precariously between legal and illegal, on open display but hidden from view.
It's also hugely popular. In sloping, bluestone-paved Hosier Lane, there are clutches of tourists day and night, taking shots of the plentiful art across its walls.
Hosier Lane has come a long way since the first years of the 21st century, when political paste-up art first started appearing on its bricks. It retains some spikiness – on one wall I spot a poster featuring Rupert Murdoch's head against crossbones, with the legend "Pirate Empire" beneath.
Though the lane is freely accessible, this artist-led tour adds layers of knowledge and expertise to its otherwise overwhelming spread of art.
At the lower end of Hosier Lane, Russell points out the intricate white scrawls surrounding the windows of Movida, a popular tapas restaurant. This patterning by an artist called Mayo, suggestive of lettering, provides a backdrop which later artists will embellish with their own work.
It's easy to become absorbed in the large murals in the lane, but our guide draws attention to smaller pieces which could be easily overlooked.
Affixed to a wall is a replica revolver with a bent barrel, the work of Sydney artist Will Coles. Coles specialises in creating thought-provoking replicas of everyday objects, and there are many of his works scattered through the Melbourne streets.
As Russell points out different types of art, we're starting to understand the differences between tags, stencils, throw-ups and paste-ups. Most people are intolerant of tags – basically a scrawled artist's name – but our guide is a defender of them. He particularly likes adjoining Rutledge Lane, which is completely "bombed" with tags.
As we leave Hosier Lane, we pass a huge depiction of an Aboriginal boy wearing face paint, high above the street on a side wall. It's beautifully rendered, the boy gazing off towards the Yarra River.
Russell then leads us to art in quieter laneways which we'd never have found for ourselves. In just one alley there's a paste-up of a girl beneath an umbrella being rained on by coloured paint; a geisha stencilled next to a doorway; a huge scatter of blue applied by a fire extinguisher; and a stencilled black rat by French artist Blek le Rat, who inspired the notorious Banksy.
Further on, I particularly like the big gramophone player attached to tank treads, painted near the opening of AC/DC Lane. "I love a good bombed doorway," says Russell, before pointing out to us an actual Banksy rat between jostling patches of paint.
Having wound our way through the city centre by back routes, we end up at Blender Studios, an alternative art hub with its own gallery and an adjacent laneway completely covered in imaginative creations.
As we sip beer and look around inside the studios, it's a chance to rest our feet and reflect on the tension between indoor and outdoor art, between big and small pieces, and between authorised and unauthorised creativity.
"You can't have one without the other," says our guide. And it's that tension that gives Melbourne's street art its edge.
Tim Richards was a guest of Melbourne Street Art Tours.