Main intercepting sewer tunnel. Unknown visitors. The tunnel still exists and the deepest shaft in the system down to the tunnel is on Stirling Ridge. One of the three surviving heritage listed sewer vents in on the ridge (red brick). The tunnel is around a couple of hundred feet below ground level at that point. The sewer tunnel begins on the Westridge side and continues under Stirling Ridge and Stirling Park over to the Provisional Parliament House area. In the Westridge area (Yarralumla) the tunnel broke into one of the many caves and had to be rerouted. There are caves under Civic Centre with underground stream. I have met people who have been the caves.