Sewers

The Zuzu City Sewers can be entered through the grates to the right of the Bus Stop, as well as through the Sanctuary bathrooms. The player does not need to have found the Rusty Key to enter. The Zuzu City sewers are also accessible via the Stardew Valley sewers.

=Mr. Qi's Shop=

Mr. Qi's shop can only be accessed by entering the stall marked "Out of Order" in the Sanctuary bathrooms. He will always sell a Qi Crystal, a Qi Blade, and a Serpent's Smallsword.

Sewer Puzzle Solution
The reward for solving the sewer puzzle is 5 Artifact Trove. Below are each of the steps needed to solve the puzzle.