Sewer Key

Sewer Key is needed to gain access to the Mind Flayer's Lair in the sewers beneath Athkatla Temple. The itself can be found in the Windspear Hills dungeon. This item appears in Baldur's Gate II: Shadows of Amn and Baldur's Gate II: Enhanced Edition.

In-game description
"This key has a faint but foul odor clinging to it, like that of the sewers. There are no sewers within the halls where you found the key. The lock that this key opens will have to be found elsewhere."