The Australian Inland Botanic Gardens are a semi-arid garden near Mildura, with native Australian plants alongside species from other dry regions of the world. The setting is a good fit for the Mallee climate, so the visit feels more specific than a generic town garden.
Come for a quiet walk among desert-adapted plantings, especially if you are interested in how gardens work in hot, dry country. It is best as a slow outdoor stop rather than a formal museum-style visit.