Umpherston Sinkhole is a collapsed limestone cave turned into a sunken garden on the eastern side of Mount Gambier. Paths and terraces lead down into the crater, where ferns, hydrangeas, and trailing plants grow against the limestone walls.
It is one of the easiest of Mount Gambier's sinkholes to visit and is especially atmospheric in the evening, when possums often come out around the garden. Pair it with Cave Garden and Blue Lake for a good introduction to the town's volcanic and limestone landscape.