I think this is a very bleached Giant Panda Snail Hedleyella falconeri shell. I photographed it on the rainforest floor in Ravensbourne National Park in south-east Queensland.
These large snails are eaten by Lyrebirds Menura spp and Noisy Pitta Pitta versicolor. They in turn eat fungi, particularly bracket fungi from the Polyporaceae family, and forage in the leaf litter of damp sub-tropical forests. They grow slowly, but once mature can be 10cm across. If fresh the shells are shades of brown with radiating irregular black bands.
Update: I am told that this is in fact Frasers Banded Snail Sphaerospira fraseri. Here are a couple of links to museum articles about this species:
Frasers Banded Snail, Queensland Museum.
Breeding of Frasers Rainforest Snail, Australian Museum.