Ainslie drains was the place...even featured in one of the early Powell vids (Animal Chin maybe?).
We used to skate the spillway that ran adjacent to the Tuggeranong Parkway at the foot of Mt. Taylor, also further along Mt. Taylor was the "Insano" HUUUGE stormwater pipe that ran all the way down under Wanniassa. :)

Yeh im hanging to visit again, too old to skate or go ferriting underground now but some good mates still there (and my old 1200 ute!)