Poisoned Poseidon

Years ago, a warlock pirate captain foolishly assaulted Baldur's Gate head-on. In the process, his ship was run aground, where it began to sink into the muck. It stayed there after he was killed; eventually, someone shored up the ground underneath it and built some tunnels out from underneath it. It was used as a tannery, as well as a Dead Three cultist base of operations, sometimes at the same time.

This is where the refugees were actually being killed during the refugee murders in Baldur's Gate. Due to all but four of the employees being dead after the party's daring midnight raid, and those remaining four being in custody of the Flaming Fist, the Poseidon is presumably not in operation at this time.