A quick guide showing how to unlock the Sewer in Stardew Valley.
To unlock the Sewers in Stardew Valley you need to donate at least 60 minerals or artifacts to the museum. As soon as you achieve that, Gunther will give you the Rusty key that gives you access to the sewers.
How to find Minerals and Artifacts
The best way to farm minerals and artifacts is to collect geodes and Omni Geode inside the skull Cavern. The drop of geodes there is abundant and you can farm quickly.
How to Donate
To donate to the museum you need to visit the library and talk to Gunther.