I'm from around the NSW/ Vic border and haven't done much like this since having children about 10yrs ago..... I used to run through drains around South West Syd and even explored a few abandoneds with friends such as the old Kelly Country building and randoms in the Southern Highlands. Been on a few private tours in Vic such as May Day Hills and the old Chiltern Theatre, they were great fun. I also vaguely remember running through bunkers as a kid somewhere around La Perouse (spelling?) but havent explored in a good while.
I'm looking to get that spark that's missing back in my life, hopefully by delving into some long forgotten ruins and/ or deep lost tunnels with my family (wife & 2 pre-teen boys)..... which raises a few questions that I will be sure to ask later as my social courage builds (introvert here).
Look forward to seeing you all out there