Pottery
From a building next to a prison, you trade cans to the inmates for pottery. You collect pottery and other prisoner artwork, and they need metal cans to make shanks and stuff, so it's a win-win arrangement.
とう
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Where do you display your prison pottery? In とうきょう, of course. とうきょう's full of fancy art museums that are more than happy to show off your quirky pottery collection.