Australian Signals Directorate got the mint to print 50c coins with a multiple layer code on it.
New, they sold out quickly at $35 each.
Second hand they’re going on eBay for up to $200 each.
A text version of the codes to be solved can be found on
https://www.asd.gov.au/75th-anniversary/events/2022-09-01-75th-anniversary-commemorative-coin
Under the heading Accessible Text Version.