From a city monument to the world's tiniest art gallery

Millions of people have walked past artist Chris Reynolds' sprawling 24-metre metal sculpture built on the site of a historic public toilet block.

The other-worldly structure at the intersection of Melbourne's Bourke and Russell streets has been a fixture of the city centre for more than three decades.

Built on the heritage site of the first public toilets opened for women in Melbourne in 1902, A History Apparatus - Vessel Craft and Beacon represents the past, present and future.

The very public work cast a spotlight on Reynolds as a young man, when he was still unsure whether he would make it in the art world.

"You think perhaps as an artist, certainly as a sculptor, that at some stage you might get the opportunity to create a monument and that happened very early for me," Reynolds told AAP.

"It was a bit bewildering because then it was like ... 'what's next?'"

He retreated to focus on his craft and helped establish a studio in a psychiatric hospital, encouraging artistic patients to maintain their creativity throughout treatment and recovery.

All the while, Reynolds became a collector, amassing an eclectic assortment of odds-and-ends on his rural property at Chewton, south of Bendigo.

"Collectors can be misconstrued with hoarders," Reynolds said.

"It's a blurry line."

Among his trove was a train conductor's booth, salvaged from a miniature private railway that was ripped out of the expansive grounds of a Northcote mansion during a renovation.

The structure - roughly the size of a phone booth - sat untouched on Reynolds' property for much of a decade, until he realised its potential for public art on a more modest scale than his city work.

What was once a play thing of a wealthy rail fanatic is now possibly the world's smallest art gallery, The Chewton Small.

The gallery will feature at the Castlemaine State Festival, housing a different lone artwork over each of the event's 10 days.

It allows Reynolds to display his works without the pressure of comparison, while viewers can have the unique experience of being a lone observer.

"These days ... what's quite fashionable are these blockbuster exhibitions where everything is competing for your attention," Reynolds said.

"As a result, you tend to just glide past things.

"Even anthropomorphising the work, imagining how the work feels, it's a bit like a beauty parade: all the paintings ... lined up on the wall and they're all vying for our attention."

The tiny gallery itself will be the first of Reynolds' sculptures to be displayed, followed by a different work each day of the festival.

Visitors will be given a small collectors' card each day, creating their own miniature artwork.

"It is often talked about that an artwork doesn't exist without an audience ... like the tree in the woods thing," Reynolds said.

"So I'm giving the observer ... the opportunity to tangibly complete the work."

The Castlemaine State Festival, celebrating its 50th year, runs from March 20, featuring performances, live music and workshops across theatres, churches and gardens.