CNN —A metro train has traveled under Sydney Harbour for the first time ever in what’s being described as “a historic first step” for the Australian city. It came over 91 years after the first steam train crossed over the Sydney Harbour Bridge back in January 1932. Courtesy NSW GovernmentThe $20.5 billion AUD (around $13.7 billion) Metro City and Southwest Line, an extension of Sydney’s Metro Northwest line, will eventually extend all the way to the suburb of Sydenham in the inner west of the city. Meanwhile, plans are also in place for a $27 billion AUD (around $18 billion) Metro West line underneath Hunter Street in the Sydney central business district. The city will have a network of four lines, 46 stations and 113 kilometers of new metro rail by 2030.