I spent many weekends in Ballarat when my exGF moved home for Uni. Never heard about an underground city, but there were a few random collapses in people's backyards, however they were old mines.
Keen to see if you find anything. I wouldn't be surprised if they have tunnels joining some buildings.
Sad about Mira's (he lives in Belgium now days). Glad I got to do it last year.
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