Can you open the sewer door and Escape through the sewer by walking?

No unfortunately not. The water has a surprise for you if you decide to try it.

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No there's a moster whk will eat you and you'll re spawn

No, you can't walk through the sewers. You have to get to boat ready, and you have to take the boat. Because, there is a monster in the water, a giant octopus-type-thing. I wouldn't recommend trying to walk through the sewers.

No you can't