Can anyone help me date this key and what type of lock it would've been used in?

It's large- eight inches long (about 21 centimeters), very solid (heavy, no hole in the end of the shaft), sightly magnetic (but not as magnetic as steel), has a lot of patina on it, shows considerable wear on the shaft and lobe, no markings on it, and seems to be made from one solid piece of metal.

I thought it might be just a decoration, but it seems like it's been used to lock and unlock something by it's wear. Also, the shaft is slightly warped (bent.)

Any info would be appreciated as I'm new at this. It's a neat old key and makes a great paperweight. My best guess is that it may be a large door lock key, maybe a old jail door.

Thanks

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