Like entering a new world, the 170-metre-long hall is jaw-dropping, conjuring sci-fi thoughts. More than 30 metres beneath North Sydney, Australia's largest underground railway cavern will buzz with thousands of commuters every hour when the second stage of Sydney's massive metro rail network opens next year.

The Sydney Metro, Australia's largest public transport project, features a complex network of tunnels that vary significantly in depth to navigate the city's unique geology and existing infrastructure. On average, the tunnels sit at a depth of about 25 to 30 meters (roughly 8 to 10 stories underground). However, the network reaches its deepest point at North Sydney, where the tunnels plunge to approximately 38 to 40 meters below the surface to safely pass beneath the bottom of Sydney Harbour. This underwater crossing was a major engineering feat, requiring tunnel boring machines to grind through high-strength sandstone while maintaining structural integrity against the immense water pressure above. In contrast, at stations like Central or Martin Place, the platforms are integrated with existing subterranean levels, placing them slightly closer to the surface. For commuters in 2026, this depth is most noticeable when using the massive, high-speed escalators required to reach the platforms. The depth was carefully calculated to ensure the metro remains insulated from street-level noise and vibrations while providing a direct, high-frequency path through the heart of the central business district.