The National Gallery of Victoria is a 10 minute stroll from Flinders Street Station.
Flinders Street bound trains depart regularly from Southern Cross Station. Check www.ptv.vic.gov.au for up-to-date train departure times.
Upon arrival at Flinders Street Station, turn right at Swanston Street and continue along St Kilda Road for 430m. You will then arrive at the National Gallery of Victoria - International Art on your right.