Sydney is constructing Australia's largest underground rail cavern beneath the northern CBD as part of the $25.3 billion Metro West project, which is expected to open in 2032 and will significantly transform city transit.

By the end of 2025, twin 2.3-kilometre tunnels will be excavated beneath Hunter Street, removing approximately 460,000 tonnes of spoil, with tunnelling machines reaching this point from the Bays precinct since May 2024.

Construction workers have uncovered the longest cavern built for Sydney's new metro rail lines, extending 320 metres beneath Pyrmont, including a 180-metre station platform and a 140-metre crossover section for trains.

The Pyrmont station, designed to resemble Victoria Cross station in North Sydney, is part of the 24-kilometre Metro West line, one of the largest rail projects globally at a cost of $65 billion, with an opening targeted for 2032.

High-pressure slurry machines are being used for the under-harbour crossings, a meticulous process that is slower but necessary for the project's engineering challenges.

The shallow depth of the cavern has required extensive support structures like shotcrete and the use of giant boring machines to complete the twin tunnels connecting Rozelle and the CBD.

The Hunter Street station features three large concrete pillars supporting the roof, multiple tunnels for passenger entry, and an additional shaft under Hunter Street with escalators and lifts for passenger movement.

The Hunter Street station will serve as a central hub, larger than Victoria Cross and Martin Place stations, capable of handling up to 40,000 passengers per hour, and will facilitate seamless transfers between heavy rail and metro lines.

Plans include constructing towers up to 60 storeys above the station, with major contracts soon to be awarded despite recent tender setbacks leaving a single consortium for construction.

The station is designed for future growth, with initial operations involving six-carriage driverless trains every four minutes, with capacity to expand to eight-car trains as demand increases.

Sydney Metro chief executive Peter Regan emphasized the challenges of tunnelling through hard and soft rock conditions under the harbour, requiring careful and precise operations.

Transport Minister John Graham announced that the new Pyrmont station will enhance connectivity, enabling a two-minute train ride to the CBD and fostering local housing and job growth.

The cavern, measuring 28 meters wide and 180 meters long, is located just six meters below a historic sandstone hotel, highlighting the project's engineering complexity and proximity to existing structures.