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Entry is Free: On our last trip to Port Macdonnell we detoured via Mount Gambier for lunch and a quick look around the Umpherston Sinkhole. Photos do not do justice to how amazing these sinkholes are, the fact that they were once huge caves underground until the chamber ceiling collapsed leaving a perfect growing environment at the bottom for what is now an amazing public garden.
Our walk down to the gardens comprised a good few steps and most people would be able to manage this without too much trouble. Once you get to the bottom there are several hidden places to find and many photo opportunities for you.
https://southaustralia.com/products/limestone-coast/attraction/umpherston-sinkhole
https://www.mountgambierpoint.com.au/attractions/umpherston-sinkhole/