At 7.30pm on Wednesday evening, Bon Iver posted something hugely exciting on Instagram and Facebook:

A photo posted by Bon Iver (@boniver) on

The puzzling graphic simply says “Melbourne, 121 Johnston St, Fitzroy, September 29 2016, 6:30pm”. It also features artwork from the American band’s new album, 22, A Million, which is slated for release on September 30. The band, led by singer-songwriter Justin Vernon, released its last album Bon Iver, Bon Iver in 2011.

The Johnston Street address is currently the site of cafe Sir Charles. A mural, featuring cryptic symbols, has been on the exterior wall of the cafe since August. Versions of these murals have appeared in locations around the world. In the past day or two, the words "Bon Iver" appeared on the Fitzroy wall.

A few hours before hinting at activity in Melbourne, the band posted something similar but with a Wisconsin address with the date and time “September 28 2016, 6:30pm”.

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Is this a guerrilla gig? We all hope so, but it's highly unlikely the band could travel and perform halfway around the world within 24 hours.

An article on a Wisconsin local news site, the town where the band is from, says an outdoor sound system will play the complete album “every two hours on Friday and Saturday, starting at 9am Friday”.

Robin Shepherd, managing director of the hospitality group that owns Sir Charles, says he happened to be in the cafe at 10pm on Wednesday night.

"The phone did not stop ringing. Everytime I hung up, it rang," he says. "I had so many funny conversations with people."

"I started answering the phone, 'Bon Iver Ticketing Agency'?" he says, laughing. "One girl gave me the full rundown on who Bon Iver is."

Shepherd says he received a call from Bon Iver's management late on Thursday morning, confirming a team will be setting up under the mural to stream the new album from 6.30pm.

Sir Charles will extend its hours to remain open for Bon Iver fans during the event.

This article was updated at 12pm, Thursday September 29.