This is a 28mm miniature locked sewer entrance 2x2 inches. This is going to be the start of stackable sewer tiles. Why not play vertically as well as horizontally? One side most likely will be open to play and the other three sides will contain terrain for future tiles.
To start into the sewer, however, you need an entrance. You don't want just anyone going into the sewers. This has doors that can be opened and closed and two types of sewer grates to cover the hole to the entrance.
Just as a warning, some assembly is required. The pivots to the doors will need to be superglued to the door. You will need to sand off a little bit of the pivots at the ends that go to the doors as well. Putting them the right size was too thin for some printers and sanding allows adjustment. Also you will need to place some type of a rod between the two holes to allow pivoting. In my case I just used some fancy plastic tooth picks.
I have also just provided the stone wall that surrounds the sewer entrance with the angled sides if you just one a simple by detailed drop terrain piece.