Green Waterhole Cave (5L81), also known as Greenwater Hole and Fossil Cave, is a cave in the Limestone Coast region of south-eastern South Australia. It lies about 22 kilometres (14 miles) north-west of the city of Mount Gambier, only a few metres from the Princes Highway (Route B1) between Mount Gambier and Millicent. It is notable both as a paleontological site and as a cave diving site.