Fernleigh Tunnel runs underneath the Pacific Highway at Adamstown Heights. It was part of the Belmont Railway Line, which ran from Adamstown to (surprise) Belmont. The railway line was closed in 1991, and in 2003 the first section containing the tunnel was re-opened as a cycleway. Today the Fernleigh Track extends all the way to Belmont.
The tunnel is a fantastic photography location, and I’ll be back soon.