This is an interesting blog (in Spanish) from Egyptologist Dr Marina Escolano-Poveda:
The nutshell version is that the History of Science Museum in Oxford has an octagonal gold box with triangular shapes protruding from it. It is a polyhedral sundial, but it's superficially very similar to the key we see in the film! I know from my own research on other props from the franchise that the prop/art department went to the British Museum in London and used objects there as reference so it's not too big a stretch to think they also went to Oxford.
Here's the object's full detail: https://www.mhs.ox.ac.uk/collection...=54054&querytype=field&thumbnails=on&irn=2978
LA LLAVE DE HAMUNAPTRA, ¿INSPIRADA EN UN RELOJ DE SOL DEL S. XVI? ð
[Nota inicial: la llave de Hamunaptra no es un objeto egipcio real. He visto que muchos lo habéis preguntado a través de redes sociales] ...
egyptologicalbibliophile.blogspot.com
The nutshell version is that the History of Science Museum in Oxford has an octagonal gold box with triangular shapes protruding from it. It is a polyhedral sundial, but it's superficially very similar to the key we see in the film! I know from my own research on other props from the franchise that the prop/art department went to the British Museum in London and used objects there as reference so it's not too big a stretch to think they also went to Oxford.
Here's the object's full detail: https://www.mhs.ox.ac.uk/collection...=54054&querytype=field&thumbnails=on&irn=2978