Soooo I found this door.

What is this?

It doesn't even lead somewhere.

Story is, I was on vacation and found this door at the boat dock.
It was night and it was ebb, so there where weird wooden posts, that looked completely black in the night. On a Industrial terrain and the wind made strange high, kind of singing noises in the wind.

And then there was this door. Behind it was a boat dock, behind the boat dock a few old boats that where swimming on the black water.
It. Was. Scary.

I was really scared, I don't know for what this door is.
left and right of it where nothing.

Please someone explain.

Please.