It's hard to tell from the photos (otherwise good) whether the underside has pores of more-or-less uniform size or whether they are irregular (tending towards maze-like) - which would be much more interesting. Would you be able to get one of these off the barrel and intact ? Then it would be easy to turn it upside down and get a photo looking straight down on the underside to see just what the arrangement is. you can see a somewhat maze-like underside in one of the photos here: https://canberra.naturemapr.org/sightings/3402388.
Heino, I have added 2 photos of the undersides - one is of the 2 shelfs lowest on the barrel in photo 3 and the other is of an older more colourful shelf from the top of the barrel rim. I think they look maze like but your judgement is needed! Barbara
Thanks for the extra photos. They're very helpful and make this an intriguing sighting. This is probably a species of either Cerrena or of Trametes (but not Trametes versicolor). I'll have to check some references.