A friend of mine was down in Tassie recently, and on their last day they decided to explore the upper part of Avon Creek before abseiling down Montezuma Falls, which at 104m is apparently the tallest waterfall in Tasmania.
Their trip report is well worth a read and includes some pretty spectacular photos: https://fatcanyoners.org/2019/02/20/montezuma-falls/
They didn't find any signs of a track to the top of the falls, or any evidence that others had explored the canyon or abseiled the falls. I'm curious if anyone knows of this trip having been done previously or if they really can claim a first descent.