Edited this model to have a sealed compartment at the top.

Still print in place. You will need to pause the print around 70mm and screw in the plate. Another option is to solve the puzzle, screw in the plate, then scramble the puzzle. The threaded compartment is reverse threaded. The 3mf includes a pause to pop off the key and plate so it can be screwed into place. Then whatever item is wanted to be hidden can be placed before contuining the print.

I remixed this to hold a NFC tag which is part of a scavenger hunt.