Hidden in the water channel. Go back to the Aqueduct Control Room. Dive (tap the water). Serpent Key is under the grate.

: This isn't a combat fight but a logic sequence. You must activate floor plates in an order that avoids the snake's gaze.

If you can describe the specific puzzle or screen you're stuck on (e.g., “three stone dials” or “a locked door with four colored gems”), I can give you a precise solution. Otherwise, a video walkthrough is your fastest bet.

: Start by interacting with the items in your immediate surroundings to find tools for a makeshift escape .

opens the right gate → gives you a hook .