How about the ruins of a Byzantine garum manufactory in Turkey - in the last batch that was ever made there, circa 1300 AD or whenever, something got hauled in with the fish that wasn't a fish - a shoggoth or deep one or sea anemone-parasitized immortal or whatever - made a very nasty batch of garum, did very nasty things to the people who ate it
How about the ruins of a Byzantine garum manufactory in Turkey - in the last batch that was ever made there, circa 1300 AD or whenever, something got hauled in with the fish that wasn't a fish - a shoggoth or deep one or sea anemone-parasitized immortal or whatever - made a very nasty batch of garum, did very nasty things to the people who ate it
t. semiurge
Byzantine Innsmouth on the Black Sea sounds good in general.