Artist Bruce Potter began the mural, which is made up of scenes from the Otago Central Rail Trail, two and a-half months ago.
He was largely given creative control of the project, he said.
``I went out on to the trail and took a whole lot of photos. I wanted to give people an idea of what they will find on it.''
The pedestrian and bicycle underpass was opened in July 2015 and cuts from the Clyde township, under State Highway 8, to near the Clyde end of the rail trail.
The project is funded by Promote Dunstan, which gave him $20,000 for one wall.
He would do the other side for about the same cost, he said.
Mr Potter said he wanted to make the mural a seamless collection of scenes, chronicling a trip on the trail.
``I'm really enjoying it, although there are certain challenges with painting on concrete.''
He has illustrated more than 120 books, but recently pivoted back to fine arts as the book industry was ``imploding on itself''.
``It's also good to have this to focus on. Selling paintings can be a mission.''
He hoped the group would find funding for him to paint the underpass entranceway to look like the entrance to a tunnel.
Promote Dunstan secretary Louise Joyce said it spent money from events it held, such as the Clyde Wine and Food Festival, on projects like this that beautify the area.
``We're thrilled to have Bruce, who is painting a wonderful mural. It looks like a photograph.''
