Mount Gambier's big-ticket item is the luminous, 75m-deep lake, which turns an insane hue of blue during summer. Perplexed scientists think it has to do with calcite crystals suspended in the water, which form at a faster rate during the warmer months. Consequently, if you visit between April and November, the lake will look much like any other − a steely grey. But in January, wow! The surface of the water is 20m below central Mt Gambier's street level.
Aquifer Tours runs hourly tours, taking you down near the lake shore in a glass-panelled lift, via an 80m tunnel. Or you can just wander around the rim of the lake along a 3.6km trail.
